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MATHEMATICS · GRADE 12

Exam Revision: Paper 1 and Paper 2 structure, ten high-yield topic clusters, condensed formula reference and exam-day strategy
CAPS-aligned · Distinction-level Notes
Mathematics · Grade 12 · Exam Revision Date: TopJournal

Every distinction begins with one topic at a time.- start now

Paper 1 · Paper 2 · Exam blueprint
BEFORE YOU WRITE · HOW THE EXAM IS BUILT EXAM FORMAT

Learning outcomes · you must be able to

📖 KEY DEFINITION Knowledge: recalling a fact, definition or formula directly, with no working needed. Routine procedures: applying a well-drilled method in a familiar, mostly single-step context. Complex procedures: combining several concepts or steps, often in a less familiar setting, using techniques you already know. Problem-solving: devising your own strategy in an unseen context where the method is not obvious from the wording.

The two papers at a glance

PaperCore topicsTotal marksDuration
Paper 1Algebra, equations & patterns; Functions & graphs; Finance, growth & decay; Differential calculus; Probability1503 hours
Paper 2Statistics; Analytical geometry; Trigonometry (identities, equations, graphs, 2D & 3D); Euclidean geometry1503 hours

How the marks divide across cognitive levels

LevelTypical weightingWhat earns these marksCommand words to expect
Knowledge20%Stating a definition, formula or fact with no calculationwrite down, state, define
Routine procedures35%A standard method applied to a familiar, mostly one-step questioncalculate, solve, determine
Complex procedures30%Several steps or concepts linked together in a less familiar settinghence, show that, prove
Problem solving15%An unseen context where you must choose your own strategyinvestigate, hence or otherwise
⚡ MUST MEMORISE

Paper 1: 150 marks, 3 hours, covers algebra & patterns, functions, finance, calculus and probability.
Paper 2: 150 marks, 3 hours, covers statistics, analytical geometry, trigonometry and Euclidean geometry.
Cognitive split: 20% knowledge, 35% routine procedures, 30% complex procedures, 15% problem solving.
Round off to two decimal places unless a question states otherwise.
Only a non-programmable, non-graphical scientific calculator is allowed.

Typical question-to-topic mapping

Paper 1, typical orderUsual topic
Q1Algebraic equations, inequalities and simultaneous equations
Q2Number patterns (arithmetic, geometric or quadratic)
Q3Series, sigma notation and convergence
Q4-Q5Functions and graphs, including the inverse function
Q6Finance: growth, decay and annuities
Q7-Q8Differential calculus, including optimisation and sketching
Q9Probability
Paper 2, typical orderUsual topic
Q1-Q2Statistics: central tendency, spread, and bivariate data
Q3Analytical geometry
Q4-Q5Trigonometric identities, equations and graphs
Q6-Q72D and 3D trigonometry (sine, cosine and area rules)
Q8-Q9Euclidean geometry: circle theorem riders and proportion

These are the typical TOPIC orders, not a fixed question count. Real papers run longer than the rows above: November 2025 set eleven questions in each paper and November 2024 set twelve in Paper 1 and eleven in Paper 2, so a topic can arrive one or two numbers later than shown. Plan by block and by mark weighting, never by question number.

The order and exact split above shifts slightly from year to year, so treat it as a planning guide, not a fixed rule.

⭐ EXAM FAVOURITE A detachable diagram or answer sheet is supplied almost every year for the same two purposes: completing or sketching a graph in Paper 1, and marking angles onto a circle for the Euclidean geometry riders in Paper 2. Learners who plan to use that sheet properly save real time.
🔥 FREQUENTLY TESTED The calculator and rounding instructions are tested indirectly in every single paper: a fully correct method that ends in the wrong number of decimal places, or a final answer produced with a forbidden calculator function, still drops the last accuracy mark on that question.
⚠️ COMMON MISTAKE Rounding a value in the middle of a multi-step calculation instead of only at the very end, which pushes the final answer outside the accepted range. Assuming a diagram is drawn to scale when the paper states it is not. Handing in a detachable diagram sheet without writing a name or candidate number on it. Using a calculator's equation-solving or graphing mode when the instructions specifically forbid it.
💡 EASY MARK Numbering an answer exactly as the question paper numbers it, giving the correct units, and rounding to two decimal places precisely as instructed cost nothing to get right, yet many capable learners still lose them through carelessness rather than a lack of knowledge.
Worked example · Splitting a question's marks by cognitive level

Q: A calculus question on a Paper 1 paper is worth 20 marks. Using the standard cognitive level weighting for the whole paper, estimate how many of those 20 marks would typically sit at each level.

Knowledge: 20% of 20 = 4 marks

Routine procedures: 35% of 20 = 7 marks

Complex procedures: 30% of 20 = 6 marks

Problem solving: 15% of 20 = 3 marks

∴ roughly 4 + 7 + 6 + 3 = 20 marks, so more than half the question (11 out of 20 marks) should be earnable through direct recall and a well-rehearsed method alone.

Read every instruction on the cover page as carefully as you read the questions themselves: a good share of the marks are hiding in how you were told to answer.- on reading the paper properly

🧠 ACTIVE RECALL
What are the total marks and duration of each Mathematics paper?(1)
Which of these topics is examined in Paper 2, not Paper 1?(1)
Unless a question says otherwise, a final numerical answer should be rounded to:(1)
Which calculator is permitted in the Mathematics exam?(1)
Which cognitive level carries the largest single share of the marks in a Mathematics paper?(2)
What must a candidate do with a detachable diagram sheet once it has been used?(1)
A full 150-mark paper follows the standard cognitive level weighting. Calculate how many marks fall under each of the four levels.(3)
Explain why numbering your answers exactly as the question paper numbers them can protect marks you have already earned.(2)
Explain this for a Grade 8: why does the exam give more marks to familiar, well-practised questions than to brand-new, tricky ones?
ONE-MINUTE SUMMARY

Paper 1 and Paper 2 are each 150 marks over 3 hours, split across a fixed set of CAPS topics. Marks are also split by cognitive level: roughly 20% knowledge, 35% routine procedures, 30% complex procedures and 15% problem solving, so most marks reward a well-drilled method, not exotic insight. Round final answers to two decimal places unless told otherwise, use only a non-programmable, non-graphical calculator, and complete any detachable diagram sheet fully before handing it in.

IN THE EXAM
  • Spend the first two minutes checking the cover page: calculator rule, rounding rule, and whether a diagram or answer sheet is attached.
  • Use roughly 1.2 minutes per mark as a pacing guide across a 150-mark, 3-hour paper, and revisit any question you skip once the rest is done.
  • Number every answer exactly as the paper does, since a marker matching your work to the memorandum can only credit what they can find in the right place.
Paper 1 · 50 marks (25 algebra + 25 patterns and series)
CHAPTER 2 · ALGEBRA, EQUATIONS & SEQUENCES ALGEBRA & PATTERNS

This block opens almost every Paper 1 and it is the biggest single allocation in the paper: 25 marks of equations and inequalities, then 25 marks of patterns and series. None of it is new content. All of it is technique under time pressure, so revise the routine for each question type rather than the full theory behind it.

Fifty marks, one third of Paper 1, and the fastest third to write. Bank it early and leave the calculus for later.

Learning outcomes · you must be able to

📖 KEY DEFINITION Number pattern: a list of numbers, called terms, generated by a fixed rule. Series: what you get when you add the terms of a pattern together. Linear (arithmetic) pattern: every term is obtained by adding the same constant d to the one before it. Geometric pattern: every term is obtained by multiplying the one before it by the same constant r. Quadratic pattern: the differences between terms are not constant, but the differences between THOSE differences are constant. Convergent series: an infinite geometric series whose running total settles on one finite number instead of growing without limit.

Mark map · where the marks actually sit in this block

Question typeTypical marksWhat the marker is looking for
Factorisable quadratic equation2 to 3Standard form first, then the factors, then BOTH roots
Quadratic formula, two decimal places3 to 4Correct a, b and c visible in the substitution; rounding only at the very end
Quadratic inequality3 to 4Critical values, a sign test, and the answer written as an interval
Simultaneous equations, linear plus quadratic5 to 6Substitution, the quadratic solved, and the answers given as PAIRS
Exponential equation3 to 4Every term rewritten to the same base before the exponents are equated
Surd equation4 to 5Isolate, square, and the written test that rejects any extraneous root
Discriminant and the nature of the roots3 to 5Δ computed correctly, then the nature stated in words
General term of an arithmetic or geometric sequence3 to 4a and d (or r) established first, then the formula
Quadratic pattern, second differences4 to 5The difference rows shown, then a, b and c solved
Sigma notation, expand or evaluate4 to 5The number of terms counted correctly, then the right sum formula
Convergence and the sum to infinity4 to 6The condition −1 < r < 1 written down explicitly
⭐ EXAM FAVOURITE The opening question is built from the same handful of blocks nearly every sitting: one quadratic that factorises, one that needs the formula and is rounded to two decimal places, one quadratic inequality, one linear-plus-quadratic simultaneous system, and one exponential or surd equation. Know the routine for each of those five cold, without stopping to think, and the first fifteen minutes of Paper 1 are already banked.

Sub-skill 1 · quadratic equations, three methods in a fixed order

Work in this order every single time and you never waste a minute deciding. First: move everything to one side so the equation reads "expression = 0". Second: try to factorise, because it is the fastest route and it carries full marks. Third: if it does not factorise neatly, reach for the quadratic formula. The phrase "correct to TWO decimal places" in the question is a direct instruction that the formula is expected, because an equation that factorises always produces exact roots that need no rounding at all.

⚠️ COMMON MISTAKE Completing the square is NOT an accepted method for solving a quadratic in this curriculum, so a solution built on it earns nothing even when the roots come out right. Completing the square stays alive in only one place: rewriting a circle's general equation in Paper 2. The other steady mark-loser is dividing both sides of an equation by x to "simplify" it, which silently destroys the root x = 0.
Worked example A · factorising, then the formula (7 marks)

Q: Solve for x: (a) 2x² − x − 15 = 0, and (b) 3x² − 8x + 2 = 0, correct to two decimal places.

(a) Already in standard form. Look for two numbers whose product is 2 × (−15) = −30 and whose sum is −1: those are −6 and +5.

2x² − 6x + 5x − 15 = 0

2x(x − 3) + 5(x − 3) = 0

(2x + 5)(x − 3) = 0

∴ x = −5⁄2 or x = 3

(b) This does not factorise, and the wording asks for two decimal places, so use the formula with a = 3, b = −8, c = 2.

Δ = b² − 4ac = (−8)² − 4(3)(2) = 64 − 24 = 40

x = [8 ± √40] ÷ 6, and √40 ≈ 6,3246

x = (8 + 6,3246) ÷ 6 = 14,3246 ÷ 6 = 2,3874…

x = (8 − 6,3246) ÷ 6 = 1,6754 ÷ 6 = 0,2792…

∴ x ≈ 2,39 or x ≈ 0,28

Mark logic: one mark for correct a, b and c inside the formula, one for the value of the discriminant, one for each rounded root. Keep full accuracy in the calculator and round only on the final line.

Sub-skill 2 · the discriminant and the nature of the roots

The discriminant Δ = b² − 4ac answers the question "what kind of roots does this equation have?" without you solving anything. The question almost always wants the answer back in WORDS, so learn the wording alongside the signs. A perfect-square discriminant means the roots are rational; a positive discriminant that is not a perfect square means they are irrational.

Value of Δ = b² − 4acNature of the rootsWhat the parabola does
Δ > 0 and a perfect squareTwo real, rational, unequal rootsCuts the x-axis at two tidy points
Δ > 0 but not a perfect squareTwo real, irrational, unequal rootsCuts the x-axis at two points that carry surds
Δ = 0Two equal real roots (one repeated root)Touches the x-axis at exactly one point
Δ < 0No real roots (the roots are non-real)Never reaches the x-axis at all
Worked example B · solving backwards from a stated nature (5 marks)

Q: Determine the value(s) of k for which x² + (k − 2)x + 9 = 0 has two equal real roots.

"Two equal real roots" translates directly into Δ = 0.

Here a = 1, b = (k − 2), c = 9

Δ = b² − 4ac = (k − 2)² − 4(1)(9) = (k − 2)² − 36

Set it equal to zero: (k − 2)² − 36 = 0

(k − 2)² = 36

k − 2 = 6 or k − 2 = −6

∴ k = 8 or k = −4

Check with k = 8: the equation becomes x² + 6x + 9 = (x + 3)², which does have the single repeated root x = −3.

⚠️ COMMON MISTAKE Two discriminant slips cost marks every sitting. The first is losing the minus sign on b: if b = −8 then b² = 64, never −64. The second is reading "two equal roots" and then writing Δ > 0; equal roots always means Δ = 0 exactly, and "two different real roots" is the one that means Δ > 0. Write the words and the symbol side by side before you start calculating.

Sub-skill 3 · quadratic inequalities and the sign test

An inequality is not an equation. It asks for an INTERVAL, not a pair of numbers. The routine is fixed: move everything to one side so the other side is zero, factorise, read off the critical values (where each factor is zero), then test the sign of the whole expression in each region those critical values carve out.

Worked example C · quadratic inequality with a sign test (4 marks)

Q: Solve for x: 3x² − 2x − 8 ≤ 0

The inequality is already in standard form with zero on the right.

Factorise: 3x² − 6x + 4x − 8 = 3x(x − 2) + 4(x − 2) = (3x + 4)(x − 2)

Critical values: 3x + 4 = 0 gives x = −4⁄3; and x − 2 = 0 gives x = 2

Now test one value in each of the three regions:

At x = −2: (3(−2) + 4)(−2 − 2) = (−2)(−4) = +8, so POSITIVE

At x = 0: (0 + 4)(0 − 2) = (4)(−2) = −8, so NEGATIVE

At x = 3: (9 + 4)(3 − 2) = (13)(1) = +13, so POSITIVE

We want where the expression is less than or equal to zero, which is the middle region, endpoints included.

∴ −4⁄3 ≤ x ≤ 2

Mark logic: one mark for correct factorising, one for both critical values, one for the sign reasoning, one for the interval in correct notation.

💡 EASY MARK When the parabola opens upwards (the coefficient of x² is positive), the answer is always BETWEEN the roots if the question asks for less than zero, and OUTSIDE the roots if it asks for greater than zero. That single sentence is usually the difference between 2 out of 4 and 4 out of 4, and it costs no extra calculation at all.

Sub-skill 4 · simultaneous equations, always substitute out of the linear one

When one equation is linear and the other is quadratic, make one variable the subject of the LINEAR equation and substitute it into the quadratic one. What you are left with is an ordinary quadratic in a single variable. The marks are lost at the end, not the start: each x-value has its OWN matching y-value, and the answer must be written as pairs.

Worked example D · a linear-plus-quadratic system (6 marks)

Q: Solve simultaneously for x and y: y − x = 3 and xy = 10

Make y the subject of the linear equation: y = x + 3

Substitute into the second equation: x(x + 3) = 10

x² + 3x = 10

x² + 3x − 10 = 0

Factorise: (x + 5)(x − 2) = 0, so x = −5 or x = 2

If x = −5, then y = −5 + 3 = −2

If x = 2, then y = 2 + 3 = 5

∴ (x ; y) = (−5 ; −2) or (x ; y) = (2 ; 5)

Check: (−5)(−2) = 10 and (2)(5) = 10, so both pairs satisfy xy = 10.

⚠️ COMMON MISTAKE The most expensive slip in a simultaneous question is finding both x-values and then calculating only ONE y-value, or shuffling the four numbers into the wrong pairings. Each x-value goes back into the LINEAR equation (never the quadratic one, which would hand you two possibilities again) to produce its own y. Write the answer as coordinate pairs, because pairs are what the marker is ticking.

Sub-skill 5 · exponential and surd equations

In an exponential equation the first move is always to rewrite every term as a power of the SAME base. Once the bases match, the exponents can be equated. Where a common factor is hiding, take it out first: an expression like 5x+2 − 5x factorises to 5x(5² − 1) and collapses instantly. In a surd equation you isolate the surd term, square both sides, and solve whatever ordinary equation remains. Squaring can invent roots that do not actually work, so testing the answers back in the original equation is not optional housekeeping, it is a mark.

Worked example E · exponential with a common factor (4 marks)

Q: Solve for x: 5x+2 − 5x = 120

Split the first term using the exponent law: 5x+2 = 5x × 5²

5x(25) − 5x(1) = 120

5x(25 − 1) = 120

24 × 5x = 120

5x = 5

∴ x = 1

Check: 5³ − 5¹ = 125 − 5 = 120, correct.

Worked example F · surd equation with an extraneous root (5 marks)

Q: Solve for x: √(2x + 7) = x + 2

The surd is already isolated, so square both sides:

2x + 7 = (x + 2)² = x² + 4x + 4

0 = x² + 2x − 3

(x + 3)(x − 1) = 0, so x = −3 or x = 1

Test x = 1: LHS = √9 = 3, RHS = 3, so it works

Test x = −3: LHS = √1 = 1, RHS = −1, so it fails

∴ x = 1 only

Why: a square root sign returns a non-negative value, so it can never equal −1.

Core content · naming the pattern family

Pattern typeHow to test itGeneral term TnSum of n terms, Sn
Linear (arithmetic)T2−T1 = T3−T2 = d, a fixed valueTn = a + (n−1)dSn = n⁄2[2a+(n−1)d]  or  n⁄2(a+l)
GeometricT2÷T1 = T3÷T2 = r, a fixed valueTn = a × rn−1Sn = a(rn−1) ÷ (r−1)
Quadratic1st differences change, but 2nd differences are fixedTn = an2 + bn + cno single formula, add the individual terms once Tn is known
⚡ MUST MEMORISE

Tn = a + (n−1)d
Sn = n⁄2[2a+(n−1)d]
Tn = a × rn−1
Sn = a(rn−1) ÷ (r−1)
S∞ = a ÷ (1−r), only when −1 < r < 1

Quadratic shortcut, no simultaneous equations required: a = (2nd difference) ÷ 2, then b = (first of the 1st differences) − 3a, then c = T1 − a − b.

Core content · sigma notation and the simultaneous equations technique

⭐ EXAM FAVOURITE Two clues, two unknowns: the paper gives you one fact about a specific term (Tq) and a separate fact about a sum of terms (Sp), then expects you to write each clue as its own equation in a and d, simplify both, and solve them simultaneously (substitution works fastest when one equation isolates a or d easily). The same two-clue setup reappears with geometric sequences using a and r, and with sigma sums that must be matched against a separately described series to find an unknown n.
🔥 FREQUENTLY TESTED Deriving Tn for a quadratic pattern (either by the a/b/c shortcut or by setting up three simultaneous equations), evaluating a sigma sum whose counter does not start at 1, and testing or applying the condition for a convergent geometric series, including finding the values of an unknown that keep a series convergent.
⚠️ COMMON MISTAKE n must be a positive whole number: reject any solution for n that comes out as a fraction or negative from a quadratic equation. Checking only one pair of consecutive terms for a common ratio and assuming the whole pattern is geometric is a common shortcut that backfires, always confirm at least two separate ratios match. When a sigma counter starts above 1, forgetting to adjust the term count (top − bottom + 1) throws off the entire sum.
💡 EASY MARK "Write down the next term" or "state whether this pattern is linear, quadratic or geometric" cost only 1 or 2 marks and need no formula, just an honest look at the differences or ratios.
Worked example 1 · Simultaneous equations from two clues

Q: A community fun run has added a fixed number of new entrants every year since it started. Across its first 14 years, the running total of entrants is 406. In its 20th year, exactly 79 people entered. Determine the number of entrants in year 1 (a) and the yearly increase (d), then state the general term Tn.

Clue 1 (the sum): S14 = 14⁄2[2a+13d] = 406, so 2a + 13d = 58 … (1)

Clue 2 (the term): T20 = a + 19d = 79, so a = 79 − 19d … (2)

Substitute (2) into (1): 2(79−19d) + 13d = 58, giving 158 − 38d + 13d = 58, so −25d = −100, meaning d = 4

Then a = 79 − 19(4) = 79 − 76 = 3

∴ a = 3, d = 4, and Tn = 3 + 4(n−1) = 4n − 1

Worked example 2 · Geometric pattern and convergence

Q: A workshop machine shaves off one quarter of a steel rod's remaining length with every pass. The rod is 80 cm long before the first pass. Determine the general term for the length shaved off on pass n, calculate the amount shaved off on the 5th pass, and determine whether the total length shaved off over infinitely many passes converges, if so, to what value.

Pass 1 shaves off 1⁄4(80) = 20 cm, leaving 60 cm. Pass 2 shaves off 1⁄4(60) = 15 cm

a = 20, r = 15⁄20 = 3⁄4

Tn = 20 × (3⁄4)n−1

T5 = 20 × (3⁄4)4 = 20 × 81⁄256 ≈ 6,33 cm

Since r = 3⁄4 and −1 < 3⁄4 < 1, the series converges

S∞ = a ÷ (1−r) = 20 ÷ (1 − 3⁄4) = 20 ÷ 1⁄4 = 80 cm

∴ T5 ≈ 6,33 cm; the series converges to S∞ = 80 cm (sensibly, exactly the rod's starting length)

Worked example 3 · Quadratic pattern, shortcut method

Q: Determine the general term of the quadratic pattern 5 ; 9 ; 15 ; 23 ; 33 ; …

First differences: 4 ; 6 ; 8 ; 10, not constant

Second differences: 2 ; 2 ; 2, constant, so this is quadratic

a = 2 ÷ 2 = 1

b = (first of the 1st differences) − 3a = 4 − 3(1) = 1

c = T1 − a − b = 5 − 1 − 1 = 3

∴ Tn = n2 + n + 3

Worked example 4 · Sigma notation with an offset counter

Q: Evaluate ∑k=620 (2k + 3).

Number of terms = 20 − 6 + 1 = 15

First term (k=6): 2(6) + 3 = 15. Last term (k=20): 2(20) + 3 = 43

This is a linear (arithmetic) series with a = 15, l = 43, n = 15

S15 = 15⁄2(a+l) = 7,5(15+43) = 7,5(58) = 435

∴ ∑k=620 (2k+3) = 435

Sub-skill 6 · building a sequence from two non-consecutive terms

The classic version of this question hands you two terms that do not sit next to each other and asks for a and d, or a and r. Write each given term out using the general formula and you immediately have two equations in two unknowns. The two families are handled differently at the crunch point: for an ARITHMETIC sequence you SUBTRACT the two equations, because that eliminates a; for a GEOMETRIC sequence you DIVIDE the two equations, because dividing cancels a and leaves a single power of r.

Arithmetic sequenceGeometric sequenceQuadratic pattern
Test that identifies itConstant first difference dConstant ratio rConstant second difference
General termTn = a + (n−1)dTn = arn−1Tn = an² + bn + c
Sum of n termsSn = n⁄2[2a + (n−1)d]Sn = a(rn−1) ÷ (r−1)Not in the curriculum
How you combine two given termsSubtract the two equationsDivide the two equationsBuild three equations from the differences
Typical trap sub-question"Which term equals 97?""Does the series converge?""Which term is the smallest?"
Worked example 5 · geometric sequence from two given terms (6 marks)

Q: The second term of a geometric sequence is 18 and the fifth term is 486. Determine a and r, then calculate the sum of the first 7 terms.

T2 = ar = 18   … (1)

T5 = ar4 = 486   … (2)

Divide (2) by (1): ar4 ÷ ar = 486 ÷ 18

r³ = 27, so r = 3

Substitute r = 3 into (1): a(3) = 18, so a = 6

S7 = a(r7 − 1) ÷ (r − 1) = 6(37 − 1) ÷ (3 − 1)

37 = 2 187, so S7 = 6(2 186) ÷ 2 = 3(2 186) = 6 558

∴ a = 6, r = 3 and S7 = 6 558

Check: the sequence runs 6 ; 18 ; 54 ; 162 ; 486 ; 1 458 ; 4 374, and the second and fifth terms are indeed 18 and 486.

Sub-skill 7 · convergence, and working the sum to infinity backwards

An infinite geometric series only settles on a finite total when −1 < r < 1. Three separate question styles grow out of that single condition. The first simply asks you to test it and then compute S∞ = a ÷ (1 − r). The second gives you a ratio written as an expression in x and asks for the values of x that keep the series convergent, which turns the condition itself into the double inequality you must solve. The third runs the formula backwards: it hands you S∞ plus one other fact and asks you to recover a or r, which usually produces a quadratic in r and therefore possibly TWO valid answers.

Worked example 6 · convergence condition in terms of x (4 marks)

Q: Determine the values of x for which the infinite series 3 + 3(2x − 1) + 3(2x − 1)² + … converges.

Each term is multiplied by (2x − 1) to give the next, so r = 2x − 1

Convergence requires −1 < r < 1, so −1 < 2x − 1 < 1

Add 1 to every part: 0 < 2x < 2

Divide every part by 2: 0 < x < 1

∴ the series converges for 0 < x < 1

Worked example 7 · the sum to infinity, run backwards (6 marks)

Q: A convergent geometric series has a sum to infinity of 45, and its second term is 10. Determine the first term and the common ratio.

From the sum to infinity: a ÷ (1 − r) = 45, so a = 45(1 − r) … (1)

From the second term: ar = 10 … (2)

Substitute (1) into (2): 45(1 − r)r = 10

45r − 45r² = 10

45r² − 45r + 10 = 0, and dividing throughout by 5 gives 9r² − 9r + 2 = 0

Factorise: (3r − 1)(3r − 2) = 0, so r = 1⁄3 or r = 2⁄3

If r = 1⁄3: a = 45(1 − 1⁄3) = 45 × 2⁄3 = 30

If r = 2⁄3: a = 45(1 − 2⁄3) = 45 × 1⁄3 = 15

Both ratios satisfy −1 < r < 1, so neither may be discarded.

∴ a = 30 with r = 1⁄3, or a = 15 with r = 2⁄3

Check: 30 × 1⁄3 = 10 and 15 × 2⁄3 = 10, so both give the required second term.

⭐ EXAM FAVOURITE "Determine the values of x for which the series converges" is close to a guaranteed appearance. The method is the same three lines every time: write the ratio r as an expression in x by dividing the second term by the first, set −1 < r < 1, then solve that double inequality. Rehearse it until it is automatic, because it is free marks with no thinking attached.

A number pattern only fools you once. Check a second gap or a second ratio, and it hands you its rule for free.- on number patterns

🧠 ACTIVE RECALL
The roots of (2x − 1)(x + 4) = 0 are:(2)
For 4x² − 12x + 9 = 0, the discriminant and the nature of the roots are:(2)
Solve for x: −3x + 2 ≥ 11(2)
Solve for x: 32x = 81(2)
The solution of (x + 1)(x − 6) < 0 is:(2)
Which type of number pattern is 8 ; 5 ; 2 ; −1 ; … ?(2)
If Tn = 6 + (n−1)(−2), then T15 equals:(2)
The geometric series 5 − 10 + 20 − 40 + … :(2)
How many terms are in ∑k=29 (5k − 4)?(2)
For the quadratic pattern 4 ; 10 ; 18 ; 28 ; …, the leading coefficient a in Tn = an2+bn+c is:(2)
S∞ can only be calculated for:(2)
The 6th term of a linear (arithmetic) sequence is 17, and the sum of its first 9 terms is 117. Determine the values of a and d.(5)
Show, using first and second differences, that 2 ; 7 ; 14 ; 23 ; 34 ; … is a quadratic pattern, and determine its general term Tn.(5)
Solve for x, correct to TWO decimal places: x² − 5x + 2 = 0(4)
Solve simultaneously for x and y: x − y = 1 and xy = 6(5)
Determine the values of p for which x² − 6x + p = 0 has NO real roots.(4)
Determine the values of x for which the infinite geometric series 4 + 4(x + 2) + 4(x + 2)² + … will converge.(4)
Explain this for a Grade 8: why isn't checking just one gap between two terms enough to prove a pattern is linear (arithmetic)?
ONE-MINUTE SUMMARY

The equations half runs to a fixed script: standard form, then factorise, then the formula if "two decimal places" appears. The discriminant Δ = b² − 4ac names the roots without solving, with Δ = 0 for equal roots and Δ < 0 for none. Inequalities want critical values, a sign test and an interval, and the sign flips whenever you multiply or divide by a negative. Simultaneous systems substitute out of the linear equation and answer in pairs. Exponentials want a common base, surds want a test back in the original equation.

Test first differences for a linear pattern, ratios for geometric, second differences for quadratic. Memorise all five boxed formulas cold. Count sigma terms as (top − bottom + 1) and read Tk straight off the expression next to the ∑ sign. When a question gives two separate clues about a sequence, write each as its own equation and solve them together, substitution is usually fastest. A geometric series only converges, and only then has an S∞, when −1 < r < 1. Always reject a solution for n that isn't a positive whole number.

IN THE EXAM
  • Where: the opening questions of Paper 1, almost without exception. Equations and inequalities carry 25 marks and patterns, sequences and series carry another 25, so this block is a third of the paper on its own.
  • Typical questions: a mixed bag of equation types first, then a general term or a sum to n terms, usually finished off with a contextual or convergence sub-question.
  • The two-clue simultaneous equations setup is the single most repeated technique in the sequences half, practise translating a word clue into an equation until it's automatic.
  • Marks reward the correct formula with substitution shown, not just a final number, always write the formula line first before you plug in values.
  • A short convergence sub-question (test it, or solve for an unknown that keeps it convergent) shows up almost every year.
  • Timing: this is the fastest third of Paper 1. Do not stall here. If a simultaneous system jams, move on and come back with fresh eyes.
  • Rounding: "two decimal places" means the quadratic formula is expected. Hold full accuracy in the calculator and round only the final root.
🔒 FUNCTIONS, LOGARITHMS & FINANCE
🔒 DIFFERENTIAL CALCULUS
🔒 PROBABILITY
🔒 ANALYTICAL GEOMETRY
🔒 TRIGONOMETRY
🔒 TRIGONOMETRIC GRAPHS
🔒

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