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A Level H2 Mathematics Geometry Trigonometry Quiz

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Questions

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A-Level Maths H2 Quiz - Geometry Trigonometry

Name: _______________________________ Class: _______________________________ Date: _______________________________ Score: ______ / 60

Duration: 1 hour 30 minutes Total Marks: 60

Instructions:

  • Answer ALL questions.
  • Write your answers in the spaces provided.
  • Show all working clearly; marks are awarded for method.
  • Unless otherwise stated, give non-exact answers to 3 significant figures.
  • You may use an approved graphing calculator (without CAS).
  • The number of marks is given in brackets [ ] at the end of each question or part question.

Section A: Trigonometric Functions and Equations (20 marks)

Answer ALL questions in this section.

1. Given that sinθ=35\sin \theta = \frac{3}{5} and θ\theta is acute, find the exact value of secθ\sec \theta. [2]

 

 

 

 


2. Solve the equation 2cos2x3sinx3=02\cos^2 x - 3\sin x - 3 = 0 for 0x3600^\circ \le x \le 360^\circ. [4]

 

 

 

 

 

 

 


3. Prove the identity sin2A1+cos2A=tanA\displaystyle \frac{\sin 2A}{1 + \cos 2A} = \tan A. [3]

 

 

 

 

 

 


4. The curve CC has equation y=3sin2x+4cos2xy = 3\sin 2x + 4\cos 2x for 0xπ0 \le x \le \pi.

(a) Express yy in the form Rsin(2x+α)R\sin(2x + \alpha), where R>0R > 0 and 0<α<π20 < \alpha < \frac{\pi}{2}, giving α\alpha in radians correct to 3 decimal places. [3]

 

 

 

 

 

(b) Hence, or otherwise, find the maximum value of yy and the smallest positive value of xx at which it occurs. [2]

 

 

 

 


5. Solve the equation tan(x+π6)=3\tan \left( x + \frac{\pi}{6} \right) = \sqrt{3} for 0x2π0 \le x \le 2\pi. [3]

 

 

 

 

 

 


6. Given that cosθ=513\cos \theta = -\frac{5}{13} and π<θ<3π2\pi < \theta < \frac{3\pi}{2}, find the exact value of sin2θ\sin 2\theta. [3]

 

 

 

 

 

 


Section B: Trigonometric Graphs and Transformations (20 marks)

Answer ALL questions in this section.

7. The diagram below shows the graph of y=f(x)y = f(x), where f(x)=acos(bx)+cf(x) = a\cos(bx) + c, for 0x2π0 \le x \le 2\pi.

The graph has maximum point (π,5)(\pi, 5) and minimum point (0,1)(0, 1).

(a) State the values of aa, bb, and cc. [3]

 

 

 

 

(b) Sketch the graph of y=2f(x)1y = 2f(x) - 1 for 0x2π0 \le x \le 2\pi, showing clearly the coordinates of the maximum and minimum points. [3]

 

 

 

 

 

 


8. The function gg is defined by g(x)=secxg(x) = \sec x for 0xπ0 \le x \le \pi, xπ2x \ne \frac{\pi}{2}.

(a) State the equations of the asymptotes of the graph of y=g(x)y = g(x). [1]

 

 

(b) Sketch the graph of y=g(x)y = g(x) for 0xπ0 \le x \le \pi, showing clearly the asymptotes and the coordinates of any points where the graph meets the axes. [3]

 

 

 

 

 

 

 


9. The curve CC has equation y=sinx+3cosxy = \sin x + \sqrt{3}\cos x for 0x2π0 \le x \le 2\pi.

(a) Express sinx+3cosx\sin x + \sqrt{3}\cos x in the form Rsin(x+α)R\sin(x + \alpha), where R>0R > 0 and 0<α<π20 < \alpha < \frac{\pi}{2}. [3]

 

 

 

 

 

(b) Hence, find the coordinates of the points where CC meets the xx-axis. [3]

 

 

 

 

 

 


10. The function hh is defined by h(x)=2sin(3xπ4)h(x) = 2\sin\left(3x - \frac{\pi}{4}\right) for 0xπ0 \le x \le \pi.

(a) State the amplitude and period of hh. [2]

 

 

 

(b) Find the exact values of xx for which h(x)=1h(x) = 1 in the given domain. [2]

 

 

 

 

 


Section C: Trigonometric Applications and Proofs (20 marks)

Answer ALL questions in this section.

11. In triangle ABCABC, AB=8AB = 8 cm, AC=6AC = 6 cm, and BAC=60\angle BAC = 60^\circ.

(a) Find the exact length of BCBC. [2]

 

 

 

 

(b) Find the area of triangle ABCABC, giving your answer in the form k3k\sqrt{3} cm2^2, where kk is an integer. [2]

 

 

 

 


12. Solve the equation sin2θ=cosθ\sin 2\theta = \cos \theta for 0θ2π0 \le \theta \le 2\pi. [4]

 

 

 

 

 

 

 

 


13. Prove that cos3θ+cosθsin3θsinθ=cotθ\displaystyle \frac{\cos 3\theta + \cos \theta}{\sin 3\theta - \sin \theta} = \cot \theta. [4]

 

 

 

 

 

 

 

 

 


14. The diagram shows triangle PQRPQR with PQ=10PQ = 10 cm, PR=7PR = 7 cm, and QPR=120\angle QPR = 120^\circ.

(a) Find the exact length of QRQR. [2]

 

 

 

 

(b) Find PQR\angle PQR, giving your answer correct to 1 decimal place. [2]

 

 

 

 

 


15. Given that tanA=34\tan A = \frac{3}{4} and tanB=512\tan B = \frac{5}{12}, where AA and BB are acute angles, find the exact value of tan(A+B)\tan(A + B). Hence, determine the value of A+BA + B in degrees. [4]

 

 

 

 

 

 

 

 


16. Prove that 1cos2xsin2x=tanx\displaystyle \frac{1 - \cos 2x}{\sin 2x} = \tan x. [2]

 

 

 

 

 


17. The function ff is defined by f(x)=sinx+cosxf(x) = \sin x + \cos x for 0x2π0 \le x \le 2\pi.

(a) Express f(x)f(x) in the form 2sin(x+π4)\sqrt{2}\sin\left(x + \frac{\pi}{4}\right). [2]

 

 

 

 

(b) Hence, solve the equation f(x)=1f(x) = 1 for 0x2π0 \le x \le 2\pi. [2]

 

 

 

 

 


18. In triangle XYZXYZ, XY=5XY = 5 cm, YZ=8YZ = 8 cm, and XYZ=30\angle XYZ = 30^\circ. Find the exact area of triangle XYZXYZ. [2]

 

 

 

 


19. Solve the equation 2sin2x+3cosx=02\sin^2 x + 3\cos x = 0 for 0x3600^\circ \le x \le 360^\circ. [4]

 

 

 

 

 

 

 

 


20. Prove that sin3AsinAcos3AcosA=2\displaystyle \frac{\sin 3A}{\sin A} - \frac{\cos 3A}{\cos A} = 2. [4]

 

 

 

 

 

 

 

 

 


END OF QUIZ

Check your work carefully.

Answers

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A-Level Maths H2 Quiz - Geometry Trigonometry: ANSWER KEY

Total Marks: 60


Section A: Trigonometric Functions and Equations (20 marks)

1. Given sinθ=35\sin \theta = \frac{3}{5}, θ\theta acute. cosθ=1sin2θ=1925=1625=45\cos \theta = \sqrt{1 - \sin^2 \theta} = \sqrt{1 - \frac{9}{25}} = \sqrt{\frac{16}{25}} = \frac{4}{5} [M1] secθ=1cosθ=54\sec \theta = \frac{1}{\cos \theta} = \frac{5}{4} [A1] [2 marks]


2. 2cos2x3sinx3=02\cos^2 x - 3\sin x - 3 = 0, 0x3600^\circ \le x \le 360^\circ. Using cos2x=1sin2x\cos^2 x = 1 - \sin^2 x: 2(1sin2x)3sinx3=02(1 - \sin^2 x) - 3\sin x - 3 = 0 22sin2x3sinx3=02 - 2\sin^2 x - 3\sin x - 3 = 0 2sin2x3sinx1=0-2\sin^2 x - 3\sin x - 1 = 0 2sin2x+3sinx+1=02\sin^2 x + 3\sin x + 1 = 0 [M1] (2sinx+1)(sinx+1)=0(2\sin x + 1)(\sin x + 1) = 0 [M1] sinx=12\sin x = -\frac{1}{2} or sinx=1\sin x = -1 For sinx=12\sin x = -\frac{1}{2}: x=210,330x = 210^\circ, 330^\circ For sinx=1\sin x = -1: x=270x = 270^\circ [A1 for all three] x=210,270,330\therefore x = 210^\circ, 270^\circ, 330^\circ [A1] [4 marks]


3. Prove sin2A1+cos2A=tanA\displaystyle \frac{\sin 2A}{1 + \cos 2A} = \tan A. LHS =2sinAcosA1+(2cos2A1)= \frac{2\sin A\cos A}{1 + (2\cos^2 A - 1)} [M1: use double angle formulas] =2sinAcosA2cos2A= \frac{2\sin A\cos A}{2\cos^2 A} [M1: simplify denominator] =sinAcosA=tanA== \frac{\sin A}{\cos A} = \tan A = RHS [A1] [3 marks]


4. y=3sin2x+4cos2xy = 3\sin 2x + 4\cos 2x, 0xπ0 \le x \le \pi.

(a) R=32+42=25=5R = \sqrt{3^2 + 4^2} = \sqrt{25} = 5 [M1] tanα=43\tan \alpha = \frac{4}{3}, so α=tan1(43)0.927\alpha = \tan^{-1}\left(\frac{4}{3}\right) \approx 0.927 rad (3 d.p.) [M1] y=5sin(2x+0.927)\therefore y = 5\sin(2x + 0.927) [A1]

(b) Maximum value of y=5y = 5 [B1] Occurs when sin(2x+0.927)=1\sin(2x + 0.927) = 1 2x+0.927=π2+2kπ2x + 0.927 = \frac{\pi}{2} + 2k\pi Smallest positive xx: 2x=π20.927=1.57080.9273=0.64352x = \frac{\pi}{2} - 0.927 = 1.5708 - 0.9273 = 0.6435 x=0.322x = 0.322 rad (3 s.f.) [A1] [5 marks]


5. tan(x+π6)=3\tan\left(x + \frac{\pi}{6}\right) = \sqrt{3}, 0x2π0 \le x \le 2\pi. tan(x+π6)=3    x+π6=π3+kπ\tan\left(x + \frac{\pi}{6}\right) = \sqrt{3} \implies x + \frac{\pi}{6} = \frac{\pi}{3} + k\pi [M1] x=π3π6+kπ=π6+kπx = \frac{\pi}{3} - \frac{\pi}{6} + k\pi = \frac{\pi}{6} + k\pi [M1] For k=0k = 0: x=π6x = \frac{\pi}{6} For k=1k = 1: x=7π6x = \frac{7\pi}{6} For k=2k = 2: x=13π6>2πx = \frac{13\pi}{6} > 2\pi (reject) x=π6,7π6\therefore x = \frac{\pi}{6}, \frac{7\pi}{6} [A1] [3 marks]


6. cosθ=513\cos \theta = -\frac{5}{13}, π<θ<3π2\pi < \theta < \frac{3\pi}{2} (third quadrant). sinθ=1cos2θ=125169=144169=1213\sin \theta = -\sqrt{1 - \cos^2 \theta} = -\sqrt{1 - \frac{25}{169}} = -\sqrt{\frac{144}{169}} = -\frac{12}{13} [M1] sin2θ=2sinθcosθ=2(1213)(513)\sin 2\theta = 2\sin \theta \cos \theta = 2\left(-\frac{12}{13}\right)\left(-\frac{5}{13}\right) [M1] =120169= \frac{120}{169} [A1] [3 marks]


Section B: Trigonometric Graphs and Transformations (20 marks)

7. f(x)=acos(bx)+cf(x) = a\cos(bx) + c, max (π,5)(\pi, 5), min (0,1)(0, 1).

(a) Amplitude =512=2= \frac{5 - 1}{2} = 2, so a=2a = 2 [B1] Vertical shift c=5+12=3c = \frac{5 + 1}{2} = 3 [B1] Period: distance from min to max is half period =π= \pi, so period =2π= 2\pi. b=2πperiod=2π2π=1b = \frac{2\pi}{\text{period}} = \frac{2\pi}{2\pi} = 1 [B1] a=2,b=1,c=3\therefore a = 2, b = 1, c = 3

(b) y=2f(x)1=2(2cosx+3)1=4cosx+61=4cosx+5y = 2f(x) - 1 = 2(2\cos x + 3) - 1 = 4\cos x + 6 - 1 = 4\cos x + 5 [M1] Max: 4(1)+5=94(1) + 5 = 9 at x=0,2πx = 0, 2\pi [A1] Min: 4(1)+5=14(-1) + 5 = 1 at x=πx = \pi [A1] Sketch: cosine curve with amplitude 4, shifted up 5. [6 marks]


8. g(x)=secxg(x) = \sec x, 0xπ0 \le x \le \pi, xπ2x \ne \frac{\pi}{2}.

(a) Asymptote: x=π2x = \frac{\pi}{2} [B1]

(b) y=secx=1cosxy = \sec x = \frac{1}{\cos x}. yy-intercept: x=0x = 0, y=sec0=1y = \sec 0 = 1 [B1] As xπ2x \to \frac{\pi}{2}^-, cosx0+\cos x \to 0^+, so y+y \to +\infty As xπ2+x \to \frac{\pi}{2}^+, cosx0\cos x \to 0^-, so yy \to -\infty At x=πx = \pi: y=secπ=1y = \sec \pi = -1 [B1] Sketch: U-shaped branch for 0x<π20 \le x < \frac{\pi}{2} with minimum at (0,1)(0, 1), approaching ++\infty at asymptote; inverted U-shaped branch for π2<xπ\frac{\pi}{2} < x \le \pi with maximum at (π,1)(\pi, -1), approaching -\infty at asymptote. [A1 for correct sketch] [4 marks]


9. y=sinx+3cosxy = \sin x + \sqrt{3}\cos x, 0x2π0 \le x \le 2\pi.

(a) R=12+(3)2=4=2R = \sqrt{1^2 + (\sqrt{3})^2} = \sqrt{4} = 2 [M1] tanα=31=3\tan \alpha = \frac{\sqrt{3}}{1} = \sqrt{3}, so α=π3\alpha = \frac{\pi}{3} [M1] sinx+3cosx=2sin(x+π3)\therefore \sin x + \sqrt{3}\cos x = 2\sin\left(x + \frac{\pi}{3}\right) [A1]

(b) CC meets xx-axis when y=0y = 0: 2sin(x+π3)=02\sin\left(x + \frac{\pi}{3}\right) = 0 sin(x+π3)=0\sin\left(x + \frac{\pi}{3}\right) = 0 [M1] x+π3=0,π,2π,3π,x + \frac{\pi}{3} = 0, \pi, 2\pi, 3\pi, \ldots x=π3,2π3,5π3,8π3,x = -\frac{\pi}{3}, \frac{2\pi}{3}, \frac{5\pi}{3}, \frac{8\pi}{3}, \ldots [M1] In domain 0x2π0 \le x \le 2\pi: x=2π3,5π3x = \frac{2\pi}{3}, \frac{5\pi}{3} Coordinates: (2π3,0)\left(\frac{2\pi}{3}, 0\right) and (5π3,0)\left(\frac{5\pi}{3}, 0\right) [A1] [6 marks]


10. h(x)=2sin(3xπ4)h(x) = 2\sin\left(3x - \frac{\pi}{4}\right), 0xπ0 \le x \le \pi.

(a) Amplitude =2= 2 [B1] Period =2π3= \frac{2\pi}{3} [B1]

(b) h(x)=1h(x) = 1: 2sin(3xπ4)=12\sin\left(3x - \frac{\pi}{4}\right) = 1 sin(3xπ4)=12\sin\left(3x - \frac{\pi}{4}\right) = \frac{1}{2} [M1] 3xπ4=π6+2kπ3x - \frac{\pi}{4} = \frac{\pi}{6} + 2k\pi or 3xπ4=5π6+2kπ3x - \frac{\pi}{4} = \frac{5\pi}{6} + 2k\pi 3x=π6+π4+2kπ=5π12+2kπ3x = \frac{\pi}{6} + \frac{\pi}{4} + 2k\pi = \frac{5\pi}{12} + 2k\pi or 3x=5π6+π4+2kπ=13π12+2kπ3x = \frac{5\pi}{6} + \frac{\pi}{4} + 2k\pi = \frac{13\pi}{12} + 2k\pi x=5π36+2kπ3x = \frac{5\pi}{36} + \frac{2k\pi}{3} or x=13π36+2kπ3x = \frac{13\pi}{36} + \frac{2k\pi}{3} For k=0k = 0: x=5π36,13π36x = \frac{5\pi}{36}, \frac{13\pi}{36} For k=1k = 1: x=5π36+2π3=29π36,13π36+2π3=37π36>πx = \frac{5\pi}{36} + \frac{2\pi}{3} = \frac{29\pi}{36}, \frac{13\pi}{36} + \frac{2\pi}{3} = \frac{37\pi}{36} > \pi (reject) x=5π36,13π36,29π36\therefore x = \frac{5\pi}{36}, \frac{13\pi}{36}, \frac{29\pi}{36} [A1] [4 marks]


Section C: Trigonometric Applications and Proofs (20 marks)

11. Triangle ABCABC: AB=8AB = 8, AC=6AC = 6, BAC=60\angle BAC = 60^\circ.

(a) Cosine rule: BC2=AB2+AC22(AB)(AC)cos60BC^2 = AB^2 + AC^2 - 2(AB)(AC)\cos 60^\circ =64+362(8)(6)(12)= 64 + 36 - 2(8)(6)\left(\frac{1}{2}\right) [M1] =10048=52= 100 - 48 = 52 BC=52=213BC = \sqrt{52} = 2\sqrt{13} cm [A1]

(b) Area =12(AB)(AC)sin60= \frac{1}{2}(AB)(AC)\sin 60^\circ =12(8)(6)(32)= \frac{1}{2}(8)(6)\left(\frac{\sqrt{3}}{2}\right) [M1] =123= 12\sqrt{3} cm2^2 [A1] [4 marks]


12. sin2θ=cosθ\sin 2\theta = \cos \theta, 0θ2π0 \le \theta \le 2\pi. 2sinθcosθ=cosθ2\sin \theta \cos \theta = \cos \theta [M1] 2sinθcosθcosθ=02\sin \theta \cos \theta - \cos \theta = 0 cosθ(2sinθ1)=0\cos \theta(2\sin \theta - 1) = 0 [M1] cosθ=0\cos \theta = 0 or sinθ=12\sin \theta = \frac{1}{2} cosθ=0\cos \theta = 0: θ=π2,3π2\theta = \frac{\pi}{2}, \frac{3\pi}{2} [A1] sinθ=12\sin \theta = \frac{1}{2}: θ=π6,5π6\theta = \frac{\pi}{6}, \frac{5\pi}{6} [A1] θ=π6,π2,5π6,3π2\therefore \theta = \frac{\pi}{6}, \frac{\pi}{2}, \frac{5\pi}{6}, \frac{3\pi}{2} [4 marks]


13. Prove cos3θ+cosθsin3θsinθ=cotθ\displaystyle \frac{\cos 3\theta + \cos \theta}{\sin 3\theta - \sin \theta} = \cot \theta.

Using sum-to-product formulas: cos3θ+cosθ=2cos(3θ+θ2)cos(3θθ2)=2cos2θcosθ\cos 3\theta + \cos \theta = 2\cos\left(\frac{3\theta + \theta}{2}\right)\cos\left(\frac{3\theta - \theta}{2}\right) = 2\cos 2\theta \cos \theta [M1] sin3θsinθ=2cos(3θ+θ2)sin(3θθ2)=2cos2θsinθ\sin 3\theta - \sin \theta = 2\cos\left(\frac{3\theta + \theta}{2}\right)\sin\left(\frac{3\theta - \theta}{2}\right) = 2\cos 2\theta \sin \theta [M1]

LHS =2cos2θcosθ2cos2θsinθ= \frac{2\cos 2\theta \cos \theta}{2\cos 2\theta \sin \theta} [M1] =cosθsinθ=cotθ== \frac{\cos \theta}{\sin \theta} = \cot \theta = RHS [A1] [4 marks]


14. Triangle PQRPQR: PQ=10PQ = 10, PR=7PR = 7, QPR=120\angle QPR = 120^\circ.

(a) Cosine rule: QR2=PQ2+PR22(PQ)(PR)cos120QR^2 = PQ^2 + PR^2 - 2(PQ)(PR)\cos 120^\circ =100+492(10)(7)(12)= 100 + 49 - 2(10)(7)\left(-\frac{1}{2}\right) [M1] =149+70=219= 149 + 70 = 219 QR=219QR = \sqrt{219} cm [A1]

(b) Sine rule: sin(PQR)PR=sin120QR\frac{\sin(\angle PQR)}{PR} = \frac{\sin 120^\circ}{QR} sin(PQR)=7×sin120219=7×32219\sin(\angle PQR) = \frac{7 \times \sin 120^\circ}{\sqrt{219}} = \frac{7 \times \frac{\sqrt{3}}{2}}{\sqrt{219}} [M1] =7322190.4096= \frac{7\sqrt{3}}{2\sqrt{219}} \approx 0.4096 PQR=sin1(0.4096)24.2\angle PQR = \sin^{-1}(0.4096) \approx 24.2^\circ (1 d.p.) [A1] [4 marks]


15. tanA=34\tan A = \frac{3}{4}, tanB=512\tan B = \frac{5}{12}, A,BA, B acute. tan(A+B)=tanA+tanB1tanAtanB\tan(A + B) = \frac{\tan A + \tan B}{1 - \tan A \tan B} [M1] =34+5121(34)(512)= \frac{\frac{3}{4} + \frac{5}{12}}{1 - \left(\frac{3}{4}\right)\left(\frac{5}{12}\right)} [M1] =912+51211548=14123348=1412×4833=14×433=5633= \frac{\frac{9}{12} + \frac{5}{12}}{1 - \frac{15}{48}} = \frac{\frac{14}{12}}{\frac{33}{48}} = \frac{14}{12} \times \frac{48}{33} = \frac{14 \times 4}{33} = \frac{56}{33} [A1] Since tan(A+B)>0\tan(A + B) > 0 and A,BA, B acute, A+BA + B is acute. A+B=tan1(5633)59.5A + B = \tan^{-1}\left(\frac{56}{33}\right) \approx 59.5^\circ (1 d.p.) Alternatively, note tan45=1\tan 45^\circ = 1 and 5633>1\frac{56}{33} > 1, so A+B>45A + B > 45^\circ. Exact: A+B=tan1(5633)A + B = \tan^{-1}\left(\frac{56}{33}\right) [A1] [4 marks]


16. Prove 1cos2xsin2x=tanx\displaystyle \frac{1 - \cos 2x}{\sin 2x} = \tan x. LHS =1(12sin2x)2sinxcosx= \frac{1 - (1 - 2\sin^2 x)}{2\sin x \cos x} [M1: use double angle formulas] =2sin2x2sinxcosx=sinxcosx=tanx== \frac{2\sin^2 x}{2\sin x \cos x} = \frac{\sin x}{\cos x} = \tan x = RHS [A1] [2 marks]


17. f(x)=sinx+cosxf(x) = \sin x + \cos x, 0x2π0 \le x \le 2\pi.

(a) R=12+12=2R = \sqrt{1^2 + 1^2} = \sqrt{2} [M1] tanα=11=1\tan \alpha = \frac{1}{1} = 1, so α=π4\alpha = \frac{\pi}{4} f(x)=2sin(x+π4)\therefore f(x) = \sqrt{2}\sin\left(x + \frac{\pi}{4}\right) [A1]

(b) f(x)=1f(x) = 1: 2sin(x+π4)=1\sqrt{2}\sin\left(x + \frac{\pi}{4}\right) = 1 sin(x+π4)=12\sin\left(x + \frac{\pi}{4}\right) = \frac{1}{\sqrt{2}} [M1] x+π4=π4+2kπx + \frac{\pi}{4} = \frac{\pi}{4} + 2k\pi or x+π4=3π4+2kπx + \frac{\pi}{4} = \frac{3\pi}{4} + 2k\pi x=0+2kπx = 0 + 2k\pi or x=π2+2kπx = \frac{\pi}{2} + 2k\pi In 0x2π0 \le x \le 2\pi: x=0,π2,2πx = 0, \frac{\pi}{2}, 2\pi [A1] [4 marks]


18. Triangle XYZXYZ: XY=5XY = 5, YZ=8YZ = 8, XYZ=30\angle XYZ = 30^\circ. Area =12(XY)(YZ)sin30= \frac{1}{2}(XY)(YZ)\sin 30^\circ [M1] =12(5)(8)(12)=10= \frac{1}{2}(5)(8)\left(\frac{1}{2}\right) = 10 cm2^2 [A1] [2 marks]


19. 2sin2x+3cosx=02\sin^2 x + 3\cos x = 0, 0x3600^\circ \le x \le 360^\circ. Using sin2x=1cos2x\sin^2 x = 1 - \cos^2 x: 2(1cos2x)+3cosx=02(1 - \cos^2 x) + 3\cos x = 0 [M1] 22cos2x+3cosx=02 - 2\cos^2 x + 3\cos x = 0 2cos2x3cosx2=02\cos^2 x - 3\cos x - 2 = 0 [M1] (2cosx+1)(cosx2)=0(2\cos x + 1)(\cos x - 2) = 0 cosx=12\cos x = -\frac{1}{2} or cosx=2\cos x = 2 (reject, since 1cosx1-1 \le \cos x \le 1) [M1] cosx=12\cos x = -\frac{1}{2}: x=120,240x = 120^\circ, 240^\circ [A1] [4 marks]


20. Prove sin3AsinAcos3AcosA=2\displaystyle \frac{\sin 3A}{\sin A} - \frac{\cos 3A}{\cos A} = 2.

LHS =sin3AcosAcos3AsinAsinAcosA= \frac{\sin 3A \cos A - \cos 3A \sin A}{\sin A \cos A} [M1] =sin(3AA)sinAcosA= \frac{\sin(3A - A)}{\sin A \cos A} [M1: using sin(PQ)=sinPcosQcosPsinQ\sin(P - Q) = \sin P \cos Q - \cos P \sin Q] =sin2AsinAcosA= \frac{\sin 2A}{\sin A \cos A} [M1] =2sinAcosAsinAcosA=2== \frac{2\sin A \cos A}{\sin A \cos A} = 2 = RHS [A1] [4 marks]


END OF ANSWER KEY