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Mathematics NSC May/June 2026 P2

50 questions answered · 150 marks · DBE

Mathematics Grade 12 NSC May/June 2026 P2 Questions and Answers

NSC Examination (May/June) May/June 2026 50 answered

Every question from the NSC Examination (May/June) (DBE, May/June 2026), with a full answer written from the Grade 12 Mathematics textbook and the official marking approach. Open a question to see its answer, or use Hide answers to practise first.

Instructions

Eleven questions, all compulsory. Show all calculations, diagrams and graphs you use, since answers alone may not earn full marks. An approved non-programmable calculator may be used unless stated otherwise; round to two decimal places unless told otherwise. Diagrams are not drawn to scale, and reasons must be given for statements in Questions 9, 10 and 11.

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Question 1

4 questions
Question 1

There are 12 players in a cricket team. The number of balls each player faced in a tournament and the number of runs each scored are given below.

Balls faced (\(x\))62111224812418089969526098115
Runs scored (\(y\))1242094188208320148158350388145165

A scatter plot of the data is also given (number of balls faced on the horizontal axis from 0 to 300, number of runs scored on the vertical axis from 0 to 400). The points rise steadily from left to right, except for the point \((95\,;\,350)\), which sits far above the rest.

Statistics (Regression and Correlation) (3)
Answer

Enter the \(x\) and \(y\) values into the calculator (statistics, linear regression mode).

\[a = 39{,}47\]\[b = 1{,}44\]

\(\hat{y} = 39{,}47 + 1{,}44x\)

Full answer and marking tips
Statistics (Regression and Correlation) (2)
Answer
\[\hat{y} = 39{,}47 + 1{,}44(150)\]\[\hat{y} = 255{,}47\]

About 255 runs (\(255{,}28\) if the unrounded calculator values are used)

Full answer and marking tips
Statistics (Regression and Correlation) (4)
Answer

Mean of \(y\):

\[\bar{y} = \frac{2344}{12} = 195{,}33\]

Standard deviation of \(y\):

\[\sigma_y = 101{,}84\]

One standard deviation above the mean:

\[195{,}33 + 101{,}84 = 297{,}17\]

Runs above \(297{,}17\): 320, 350 and 388

3 players

Full answer and marking tips
Statistics (Regression and Correlation) (1)
Answer

This player scored far more runs than the other players who faced a similar number of balls (about 90 to 100 balls gave about 145 to 160 runs).

Full answer and marking tips

Question 2

5 questions
Question 2

2.1 Marks (as a %) of Grade 12 learners at a school in the June 2025 Mathematics examination:

Class interval (%)Frequency
\(20 \lt x \leq 30\)8
\(30 \lt x \leq 40\)14
\(40 \lt x \leq 50\)16
\(50 \lt x \leq 60\)21
\(60 \lt x \leq 70\)16
\(70 \lt x \leq 80\)9
\(80 \lt x \leq 90\)6
\(90 \lt x \leq 100\)2

2.2 A box and whisker diagram shows the marks (as a %) of learners at another school in the same examination. The five values labelled from left to right are: minimum \((x - 2)\%\), lower quartile \(\left(\frac{3x - 3}{2}\right)\%\), median \((2x + 5)\%\), upper quartile \((3x)\%\) and maximum \(91\%\).

Statistics (Regression and Correlation) (1)
Answer

The highest frequency is 21.

\(50 \lt x \leq 60\)

Full answer and marking tips
Statistics (Regression and Correlation) (2)
Answer

Add each frequency to the running total:

Class interval (%)FrequencyCumulative frequency
\(20 \lt x \leq 30\)88
\(30 \lt x \leq 40\)1422
\(40 \lt x \leq 50\)1638
\(50 \lt x \leq 60\)2159
\(60 \lt x \leq 70\)1675
\(70 \lt x \leq 80\)984
\(80 \lt x \leq 90\)690
\(90 \lt x \leq 100\)292

Cumulative frequencies: 8; 22; 38; 59; 75; 84; 90; 92

Full answer and marking tips
Statistics (Regression and Correlation) (3)
Answer

Ground the curve at \((20\,;\,0)\), the lower boundary of the first class.

Plot each cumulative frequency at the upper boundary of its class: \((30\,;\,8)\), \((40\,;\,22)\), \((50\,;\,38)\), \((60\,;\,59)\), \((70\,;\,75)\), \((80\,;\,84)\), \((90\,;\,90)\), \((100\,;\,92)\).

Join the points with a smooth, increasing S-shaped curve.

Ogive from \((20\,;\,0)\) rising through the plotted points to \((100\,;\,92)\).

Full answer and marking tips
Statistics (Regression and Correlation) (1)
Answer

\(n = 92\), so the median is at a cumulative frequency of:

\[\frac{92}{2} = 46\]

Read across from 46 to the curve and down to the \(x\)-axis.

\(\text{Median} \approx 54\%\)

Full answer and marking tips
Statistics (Regression and Correlation) (3)
Answer
\[IQR = Q_3 - Q_1\]\[3x - \frac{3x - 3}{2} = 45\]\[6x - 3x + 3 = 90\]\[3x = 87\]\[x = 29\]\[\text{Minimum} = (x - 2)\% = (29 - 2)\%\]

\(27\%\)

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Question 3

5 questions
Question 3

AS intersects the \(y\)-axis at \(C(0\,;\,6)\). \(B(-4\,;\,8)\) is the midpoint of AC. F is the point \((0\,;\,-6)\). LF is drawn parallel to AS and cuts the \(x\)-axis at G. E is a point on LF such that the equation of AE is \(y = -\frac{7}{2}x - 18\). AE cuts the \(x\)-axis at T. SF is drawn.

Diagram: A lies in the second quadrant above B, with line AS sloping down to the right through B and C to S in the first quadrant. Line LF runs parallel to AS below it, from L (upper left, beyond G) through G on the negative \(x\)-axis and E (third quadrant) to F on the negative \(y\)-axis. Line AE runs steeply down from A through T on the negative \(x\)-axis (between G and O) to E. Segment SF joins S to F.

Analytical Geometry (3)
Answer

B is the midpoint of AC:

\[\frac{x_A + 0}{2} = -4 \quad\therefore x_A = -8\]\[\frac{y_A + 6}{2} = 8 \quad\therefore y_A = 10\]

\(A(-8\,;\,10)\)

Full answer and marking tips
Analytical Geometry (3)
Answer
\[m_{AS} = \frac{8 - 6}{-4 - 0} = -\frac{1}{2}\]\[m_{LF} = m_{AS} = -\frac{1}{2}\]

(\(LF \parallel AS\))

\(F(0\,;\,-6)\) is the \(y\)-intercept, so \(c = -6\)

\(y = -\frac{1}{2}x - 6\)

Full answer and marking tips
Analytical Geometry (3)
Answer

E lies on AE and LF, so equate:

\[-\frac{1}{2}x - 6 = -\frac{7}{2}x - 18\]\[-x - 12 = -7x - 36\]\[6x = -24\]\[x = -4\]\[y = -\frac{1}{2}(-4) - 6 = -4\]

\(E(-4\,;\,-4)\)

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Analytical Geometry (5)
Answer
\[m_{AS} = -\frac{1}{2}\]\[m_{FS} = \frac{\frac{18}{5} - (-6)}{\frac{24}{5} - 0} = \frac{\frac{48}{5}}{\frac{24}{5}} = 2\]\[m_{AS} \times m_{FS} = -\frac{1}{2} \times 2 = -1\]

so \(C\hat{S}F = 90^\circ\)

\(\therefore\) CF is a diameter (chord subtends a right angle at the circle)

Centre = midpoint of CF = \(O(0\,;\,0)\) and \(r = 6\)

\(x^2 + y^2 = 36\)

Full answer and marking tips
Analytical Geometry (4)
Answer
\[\tan(A\hat{T}X) = m_{AE} = -\frac{7}{2}\]

so the inclination of AE is \(105{,}95^\circ\)

\(\therefore G\hat{T}E = 105{,}95^\circ\) (vertically opposite the inclination angle at T)

\[\tan(L\hat{G}X) = m_{LF} = -\frac{1}{2}\]

so the inclination of LF is \(L\hat{G}T = 153{,}43^\circ\)

In \(\triangle GTE\): \(L\hat{G}T = G\hat{T}E + G\hat{E}T\) (ext \(\angle\) of \(\triangle\))

\[G\hat{E}T = 153{,}43^\circ - 105{,}95^\circ\]

\(A\hat{E}G = 47{,}49^\circ\)

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Question 4

7 questions
Question 4

The circle with centre M has equation \((x - 2)^2 + (y - 4)^2 = 25\). Diameter TMR and tangent SR are drawn. The equation of line ST is \(y = 2x + 5\). ST cuts the circle again at V. VR is drawn.

Diagram: T is on the circle at the lower left, R at the upper right end of the diameter through M. Line ST rises steeply from T through V (top of the circle) to S, where it meets the tangent at R.

Analytical Geometry (2)
Answer

Compare with \((x - a)^2 + (y - b)^2 = r^2\).

\(M(2\,;\,4)\)

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Analytical Geometry (4)
Answer

Substitute \(y = 2x + 5\) into the circle:

\[(x - 2)^2 + (2x + 5 - 4)^2 = 25\]\[x^2 - 4x + 4 + 4x^2 + 4x + 1 - 25 = 0\]\[5x^2 - 20 = 0\]\[x^2 - 4 = 0\]\[(x - 2)(x + 2) = 0\]\[x = 2 \text{ or } x = -2\]

At T, \(x = -2\):

\[y = 2(-2) + 5 = 1\]

\(\therefore T(-2\,;\,1)\)

Full answer and marking tips
Analytical Geometry (2)
Answer

From 4.2 the other intersection has \(x = 2\):

\[y = 2(2) + 5 = 9\]

\(V(2\,;\,9)\)

Full answer and marking tips
Analytical Geometry (2)
Answer
\[m_{TR} = m_{TM} = \frac{4 - 1}{2 - (-2)}\]

\(m_{TR} = \frac{3}{4}\)

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Analytical Geometry (5)
Answer

M is the midpoint of TR:

\[x_R = 2(2) - (-2) = 6\]\[y_R = 2(4) - 1 = 7\]

so \(R(6\,;\,7)\)

\[m_{SR} = -\frac{4}{3}\]

(tangent \(\perp\) radius)

\[y - 7 = -\frac{4}{3}(x - 6)\]\[y = -\frac{4}{3}x + 8 + 7\]

\(y = -\frac{4}{3}x + 15\)

Full answer and marking tips
Analytical Geometry (6)
Answer

Centre N = midpoint of AC:

\[N = \left(\frac{-3 + 2}{2}\,;\,\frac{-1 + 3}{2}\right) = \left(-\frac{1}{2}\,;\,1\right)\]\[AC = \sqrt{(2 - (-3))^2 + (3 - (-1))^2} = \sqrt{41}\]

so \(r = \frac{\sqrt{41}}{2}\) and \(r^2 = \frac{41}{4}\)

\[\left(x + \frac{1}{2}\right)^2 + (y - 1)^2 = \frac{41}{4}\]\[x^2 + x + \frac{1}{4} + y^2 - 2y + 1 = \frac{41}{4}\]\[x^2 + x + y^2 - 2y - 9 = 0\]

At the intersection points both equations hold, so equate:

\[x^2 + x + y^2 - 2y - 9 = x^2 - 4x + y^2 - 8y - 5\]\[5x + 6y - 4 = 0\]

\(6y + 5x - 4 = 0\), i.e. \(y = -\frac{5}{6}x + \frac{2}{3}\)

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Analytical Geometry (1)
Answer
\[(x - 2)^2 + (y - 4)^2 = 25 - k\]\[0 \lt 25 - k \lt 25\]

The radius becomes smaller (the circle shrinks; the centre stays at M).

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Question 5

4 questions
Trigonometry (Compound Angles, Identities, Equations) (2)
Answer
\[\sin(A + B) = \sin[A - (-B)]\]\[= \sin A\cos(-B) - \cos A\sin(-B)\]\[= \sin A\cos B - \cos A(-\sin B)\]

\(\sin(A + B) = \sin A\cos B + \cos A\sin B\)

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Trigonometry (Compound Angles, Identities, Equations) (4)
Answer
\[\sqrt{3}\cos x = \sin[(50^\circ + x) + (10^\circ - x)]\]\[\sqrt{3}\cos x = \sin 60^\circ\]\[\sqrt{3}\cos x = \frac{\sqrt{3}}{2}\]\[\cos x = \frac{1}{2}\]

Reference angle \(= 60^\circ\); \(\cos\) is positive in quadrants 1 and 4

\(x = 60^\circ\) or \(x = 300^\circ\)

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Trigonometry (Compound Angles, Identities, Equations) (5)
Answer
\[\text{LHS} = \frac{2\sin x\cos x}{2\cos^2 x} + \frac{\sin x}{\frac{\sin x}{\cos x}(1 + \sin x)}\]\[= \frac{\sin x}{\cos x} + \frac{\cos x}{1 + \sin x}\]\[= \frac{\sin x(1 + \sin x) + \cos^2 x}{\cos x(1 + \sin x)}\]\[= \frac{\sin x + \sin^2 x + \cos^2 x}{\cos x(1 + \sin x)}\]\[= \frac{\sin x + 1}{\cos x(1 + \sin x)}\]\[= \frac{1}{\cos x}\]

LHS = RHS

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Trigonometry (Compound Angles, Identities, Equations) (4)
Answer
\[\text{LHS} = \sin 260^\circ = \sin(180^\circ + 80^\circ) = -\sin 80^\circ\]\[= -\cos 10^\circ\]\[\text{RHS} = -\sqrt{\frac{2\cos^2 10^\circ - 1 + 1}{2}}\]\[= -\sqrt{\cos^2 10^\circ}\]\[= -\cos 10^\circ\]

(\(\cos 10^\circ \gt 0\))

LHS = RHS

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Question 6

3 questions
Trigonometry (Compound Angles, Identities, Equations) (5)
Answer

\(\cos 330^\circ = \cos 30^\circ\), \(\cos 365^\circ = \cos 5^\circ\), \(\sin 175^\circ = \sin 5^\circ\), \(\sin 210^\circ = -\sin 30^\circ\)

\[\text{Expression} = \cos 30^\circ\cos 5^\circ + \sin 5^\circ(-\sin 30^\circ)\]\[= \cos 30^\circ\cos 5^\circ - \sin 30^\circ\sin 5^\circ\]\[= \cos(30^\circ + 5^\circ)\]

\(= \cos 35^\circ\)

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Trigonometry (Compound Angles, Identities, Equations) (3)
Answer

\(\cos 35^\circ = p\), so draw a right triangle with hypotenuse 1 and adjacent side \(p\); the third side is \(\sqrt{1 - p^2}\), so:

\[\sin 35^\circ = \sqrt{1 - p^2}\]\[\sin 70^\circ = \sin 2(35^\circ) = 2\sin 35^\circ\cos 35^\circ\]

\(\sin 70^\circ = 2p\sqrt{1 - p^2}\)

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Trigonometry (Compound Angles, Identities, Equations) (6)
Answer
\[2^{3\sin^2 x} = 4\cdot 2^{\sin x} = 2^2\cdot 2^{\sin x} = 2^{\sin x + 2}\]\[3\sin^2 x = \sin x + 2\]\[3\sin^2 x - \sin x - 2 = 0\]\[(3\sin x + 2)(\sin x - 1) = 0\]\[\sin x = -\frac{2}{3} \text{ or } \sin x = 1\]

\(\sin x = 1\) is rejected, since \(\sin x \lt 0\)

Reference angle \(= 41{,}81^\circ\); \(\sin\) is negative in quadrants 3 and 4

\(x = 221{,}81^\circ + k\cdot 360^\circ\) or \(x = 318{,}19^\circ + k\cdot 360^\circ\), \(k \in \mathbb{Z}\)

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Question 7

6 questions
Question 7

The graph of \(f(x) = 2\sin(x - 45^\circ)\) is drawn for \(x \in [-180^\circ\,;\,180^\circ]\). The \(y\)-axis is marked from \(-3\) to \(3\) and the \(x\)-axis at \(-180^\circ\), \(-90^\circ\), \(90^\circ\) and \(180^\circ\).

Diagram: \(f\) has a minimum value of \(-2\) at \(x = -45^\circ\) and a maximum value of \(2\) at \(x = 135^\circ\). It cuts the \(x\)-axis at \(x = -135^\circ\) and \(x = 45^\circ\), and the \(y\)-axis at \(-\sqrt{2}\).

Trigonometry (Compound Angles, Identities, Equations) (1)
Answer

Amplitude = 2

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Trigonometry (Compound Angles, Identities, Equations) (2)
Answer

\(f'(x) \geq 0\) where \(f\) is increasing (or stationary): from the minimum at \(x = -45^\circ\) to the maximum at \(x = 135^\circ\).

\(-45^\circ \leq x \leq 135^\circ\)

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Trigonometry (Compound Angles, Identities, Equations) (3)
Answer

Asymptotes: \(x = -90^\circ\) and \(x = 90^\circ\) (dotted vertical lines).

\(x\)-intercepts: \((-180^\circ\,;\,0)\), \((0^\circ\,;\,0)\) and \((180^\circ\,;\,0)\).

Points: \(g(-135^\circ) = -1\), \(g(-45^\circ) = 1\), \(g(45^\circ) = -1\), \(g(135^\circ) = 1\).

Shape: the tan graph reflected in the \(x\)-axis, so each branch decreases from left to right: one branch from \((-180^\circ\,;\,0)\) down towards \(x = -90^\circ\), a middle branch from top left near \(x = -90^\circ\) through \((0^\circ\,;\,0)\) to bottom right near \(x = 90^\circ\), and a branch from the top near \(x = 90^\circ\) down to \((180^\circ\,;\,0)\).

Three decreasing branches of \(-\tan x\) with asymptotes at \(x = \pm 90^\circ\) and \(x\)-intercepts at \(-180^\circ\), \(0^\circ\) and \(180^\circ\).

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Trigonometry (Compound Angles, Identities, Equations) (1)
Answer
\[g(-45^\circ) = -\tan(-45^\circ) = 1\]\[f(-45^\circ) = 2\sin(-90^\circ) = -2\]\[1 - (-2) = 3\]

\(3\)

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Trigonometry (Compound Angles, Identities, Equations) (1)
Answer

Count the points where the graphs of \(g\) and \(f\) intersect.

2

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Trigonometry (Compound Angles, Identities, Equations) (2)
Answer

The asymptotes of \(g\) at \(x = -90^\circ\) and \(x = 90^\circ\) move \(45^\circ\) to the right (\(x = -270^\circ\) moves to \(-225^\circ\), outside the interval).

\(x = -45^\circ\) and \(x = 135^\circ\)

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Question 8

3 questions
Question 8

8.1 \(\triangle RTP\) is drawn with T at the origin and P on the positive \(x\)-axis; R lies above the \(x\)-axis. \(RT = p\) and \(RP = t\).

8.2 D, B and C are points in the same horizontal plane. AB is a vertical flagpole with \(AB = 4\) units. A rope is tied from A, the top of the flagpole, to C. \(B\hat{A}C = B\hat{C}D = \theta\) and \(B\hat{D}C = \alpha\).

Diagram: A is directly above B. Triangle BDC lies flat on the ground, and the rope AC joins the top of the pole to C.

Trigonometry (Compound Angles, Identities, Equations) (4)
Answer

Construction: draw \(RK \perp TP\) with K on TP, and let \(RK = h\).

In \(\triangle RKT\):

\[\sin\hat{T} = \frac{h}{p} \quad\therefore h = p\sin\hat{T}\]

In \(\triangle RKP\):

\[\sin\hat{P} = \frac{h}{t} \quad\therefore h = t\sin\hat{P}\]\[\therefore p\sin\hat{T} = t\sin\hat{P}\]

Divide both sides by \(pt\):

\(\dfrac{\sin\hat{T}}{t} = \dfrac{\sin\hat{P}}{p}\)

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Trigonometry (Compound Angles, Identities, Equations) (1)
Answer

In right-angled \(\triangle ABC\) (AB vertical):

\[\tan\theta = \frac{BC}{AB} = \frac{BC}{4}\]

\(BC = 4\tan\theta\)

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Trigonometry (Compound Angles, Identities, Equations) (5)
Answer

In \(\triangle BDC\): \(D\hat{B}C = 180^\circ - (\alpha + \theta)\) (sum of \(\angle\)s in \(\triangle\))

\[\frac{DC}{\sin[180^\circ - (\alpha + \theta)]} = \frac{BC}{\sin\alpha}\]

(sine rule)

\[DC = \frac{4\tan\theta\sin(\alpha + \theta)}{\sin\alpha}\]\[= \frac{4\tan\theta(\sin\alpha\cos\theta + \cos\alpha\sin\theta)}{\sin\alpha}\]\[= \frac{4\sin\theta(\sin\alpha\cos\theta + \cos\alpha\sin\theta)}{\cos\theta\sin\alpha}\]\[= 4\sin\theta\left[\frac{\sin\alpha\cos\theta}{\cos\theta\sin\alpha} + \frac{\cos\alpha\sin\theta}{\cos\theta\sin\alpha}\right]\]\[= 4\sin\theta\left(1 + \frac{\tan\theta}{\tan\alpha}\right)\]

\(DC = 4\sin\theta\left(1 + \dfrac{\tan\theta}{\tan\alpha}\right)\)

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Question 9

4 questions
Question 9

9.1 O is the centre of the circle. RSTV is a cyclic quadrilateral, with R and T opposite each other.

9.2 A, B, C, D and E lie on a circle. BA is produced to F. \(\hat{B}_2 = 27^\circ\) and \(\hat{C} = 88^\circ\). AE, ED, DC, BC, BE and BD are drawn.

Angle labels in 9.2: at B, \(\hat{B}_1 = \angle ABE\), \(\hat{B}_2 = \angle EBD\), \(\hat{B}_3 = \angle DBC\). At E, \(\hat{E}_1 = \angle AEB\) and \(\hat{E}_2 = \angle BED\). At D, \(\hat{D}_1 = \angle EDB\) and \(\hat{D}_2 = \angle BDC\). At A, \(\hat{A}_1 = \angle BAE\) and \(\hat{A}_2 = \angle FAE\) (outside the circle). \(\hat{C} = \angle BCD = 88^\circ\).

Euclidean Geometry (5)
Answer

Construction: draw radii OS and OV. Let \(\hat{O}_1\) be the angle at O facing T and \(\hat{O}_2\) the reflex angle at O facing R.

  1. \(\hat{O}_2 = 2\hat{R}\) (\(\angle\) at centre = 2 \(\times\) \(\angle\) at circumference)
  2. \(\hat{O}_1 = 2\hat{T}\) (\(\angle\) at centre = 2 \(\times\) \(\angle\) at circumference)
  3. \(\hat{O}_1 + \hat{O}_2 = 360^\circ\) (\(\angle\)s round a pt)
  4. \(2\hat{R} + 2\hat{T} = 360^\circ\)
  5. \(\therefore \hat{R} + \hat{T} = 180^\circ\)

\(\hat{R} + \hat{T} = 180^\circ\)

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Euclidean Geometry (2)
Answer
  1. \(\hat{E}_2 + \hat{C} = 180^\circ\) (opp \(\angle\)s of cyclic quad BCDE)
  2. \(\hat{E}_2 = 180^\circ - 88^\circ\)

\(\hat{E}_2 = 92^\circ\)

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Euclidean Geometry (2)
Answer
  1. \(\hat{B}_3 = \hat{B}_2\) (equal chords; equal \(\angle\)s)

\(\hat{B}_3 = 27^\circ\)

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Euclidean Geometry (3)
Answer
  1. \(\hat{D}_1 = 180^\circ - 27^\circ - 92^\circ = 61^\circ\) (sum of \(\angle\)s in \(\triangle BED\))
  2. \(\hat{A}_2 = \hat{D}_1\) (ext \(\angle\) of cyclic quad ABDE)

\(\hat{A}_2 = 61^\circ\)

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Question 10

5 questions
Question 10

O is the centre of the circle. Chord AS is perpendicular to diameter BOD at K. OR is drawn with R on BS. AB, AD and OS are drawn. \(\hat{B}_1 = x\).

Angle labels: \(\hat{B}_1 = \angle ABD\), \(\hat{B}_2 = \angle DBS\). \(\hat{A}_1 = \angle BAS\), \(\hat{A}_2 = \angle SAD\). \(\hat{K}_3 = \angle OKS\) (\(= 90^\circ\)). \(\hat{O}_1 = \angle BOR\), \(\hat{O}_2 = \angle ROS\), \(\hat{O}_3 = \angle SOK\). \(\hat{S}_1 = \angle OSK\), \(\hat{S}_2 = \angle OSR\). \(\hat{R}_1 = \angle ORB\), \(\hat{R}_2 = \angle ORS\).

Euclidean Geometry (1)
Answer

... equal.

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Euclidean Geometry (3)
Answer
  1. \(D\hat{A}B = 90^\circ\) (\(\angle\) in semi-circle)
  2. \(\hat{D} = 180^\circ - 90^\circ - x\) (sum of \(\angle\)s in \(\triangle ABD\))

\(\hat{D} = 90^\circ - x\)

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Euclidean Geometry (3)
Answer
  1. \(\hat{S}_1 + \hat{S}_2 = \hat{D} = 90^\circ - x\) (\(\angle\)s in the same segment)
  2. In \(\triangle BKS\): \(\hat{K}_3 = 90^\circ\) (given \(AS \perp BD\))
  3. \(\hat{B}_2 = 180^\circ - 90^\circ - (90^\circ - x)\) (sum of \(\angle\)s in \(\triangle\))

\(\hat{B}_2 = x\)

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Euclidean Geometry (2)
Answer
  1. \(\hat{S}_2 = \hat{B}_2 = x\) (\(\angle\)s opp equal sides; \(OB = OS\))
  2. \(\hat{S}_1 = (\hat{S}_1 + \hat{S}_2) - \hat{S}_2 = 90^\circ - x - x\)

\(\hat{S}_1 = 90^\circ - 2x\)

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Euclidean Geometry (3)
Answer
  1. \(\hat{R}_2 = 90^\circ\) (line from centre to midpt of chord)
  2. \(\hat{K}_3 = 90^\circ\) (given \(AS \perp BD\))
  3. \(\hat{R}_2 + \hat{K}_3 = 180^\circ\)
  4. \(\therefore\) OKSR is a cyclic quadrilateral (converse opp \(\angle\)s of cyclic quad)

OKSR is cyclic.

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Question 11

4 questions
Question 11

FA is a common tangent at A to the larger circle ABC and the smaller circle ADE. Chords AB and AC of the larger circle cut the smaller circle at D and E respectively. BC is drawn. Another tangent from C meets FA produced at G. DE produced meets tangent GC at H.

Angle labels: \(\hat{A}_1 = \angle FAD\), \(\hat{A}_2 = \angle DAE\) (\(= \angle BAC\)), \(\hat{A}_3 = \angle EAG\). \(\hat{D}_1 = \angle ADE\), \(\hat{D}_2 = \angle EDB\). \(\hat{E}_1 = \angle AED\), \(\hat{E}_2 = \angle DEC\), \(\hat{E}_3 = \angle CEH\), \(\hat{E}_4 = \angle HEA\). \(\hat{C}_1 = \angle BCA\), \(\hat{C}_2 = \angle ACH\). \(\hat{H}_1 = \angle CHE\), \(\hat{H}_2 = \angle EHG\).

Euclidean Geometry (4)
Answer

In \(\triangle ADE\) and \(\triangle ABC\):

  1. \(\hat{A}_2 = \hat{A}_2\) (common)
  2. \(\hat{E}_1 = \hat{A}_1\) (tan chord theorem, small circle)
  3. \(\hat{C}_1 = \hat{A}_1\) (tan chord theorem, large circle)
  4. \(\therefore \hat{E}_1 = \hat{C}_1\)
  5. \(\hat{D}_1 = \hat{B}\) (third \(\angle\) of \(\triangle\), or tan chord theorem using \(\hat{A}_3\))
  6. \(\therefore \triangle ADE \,|||\, \triangle ABC\) (\(\angle\angle\angle\))

\(\triangle ADE \,|||\, \triangle ABC\)

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Euclidean Geometry (4)
Answer
  1. \(\hat{D}_1 = \hat{B}\) (proved in 11.1), so \(DE \parallel BC\) (corresp \(\angle\)s =)
  2. \(\dfrac{AD}{DB} = \dfrac{AE}{EC}\) (line \(\parallel\) one side of \(\triangle\))
  3. \(AD = k\), \(AB = 3k\), so \(DB = 2k\)
  4. \(\dfrac{k}{2k} = \dfrac{4}{EC}\)
  5. \(EC = 8\)

\(EC = 8\) cm

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Euclidean Geometry (4)
Answer

In \(\triangle ECH\) and \(\triangle CBA\):

  1. \(\hat{E}_3 = \hat{C}_1\) (alt \(\angle\)s; \(BC \parallel DH\))
  2. \(\hat{C}_2 = \hat{B}\) (tan chord theorem)
  3. \(\hat{H}_1 = \hat{A}_2\) (sum of \(\angle\)s in \(\triangle\))
  4. \(\therefore \triangle ECH \,|||\, \triangle CBA\) (\(\angle\angle\angle\))
  5. \(\therefore \dfrac{EH}{CA} = \dfrac{EC}{CB}\) (\(|||\) \(\triangle\)s)

\(\therefore \dfrac{EH}{EC} = \dfrac{CA}{CB}\)

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Euclidean Geometry (5)
Answer
  1. \(\dfrac{EH}{EC} = \dfrac{CA}{CB}\) (proved in 11.3), so \(EC = \dfrac{EH\cdot CB}{CA}\)
  2. \(\dfrac{EC}{AC} = \dfrac{BD}{AB}\) (line \(\parallel\) one side of \(\triangle\); \(DE \parallel BC\)), so \(EC = \dfrac{AC\cdot BD}{AB}\)
  3. \(EC \times EC = \dfrac{EH\cdot CB}{AC} \times \dfrac{AC\cdot BD}{AB}\)
  4. \(EC^2 = \dfrac{EH\cdot CB\cdot DB}{AB}\)
  5. \(EC^2 = \dfrac{EH\cdot CB\cdot DB}{3AD}\) (\(AD : AB = 1 : 3\), so \(AB = 3AD\))

\(\therefore EC = \sqrt{\dfrac{EH\cdot CB\cdot DB}{3AD}}\)

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