CAIE P2 2021 March — Question 2 5 marks

Exam BoardCAIE
ModuleP2 (Pure Mathematics 2)
Year2021
SessionMarch
Marks5
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicReciprocal Trig & Identities
TypeSolve equation with reciprocal functions
DifficultyStandard +0.3 This question requires converting reciprocal trig functions to standard form (sec²θ = 1/cos²θ, cot θ = cos θ/sin θ), simplifying to get 1/(cos θ sin²θ) = 8, then using sin²θ = 1 - cos²θ to form a cubic equation in cos θ. While it involves multiple steps and algebraic manipulation, it follows a standard pattern for reciprocal trig equations with no novel insight required, making it slightly easier than average.
Spec1.05h Reciprocal trig functions: sec, cosec, cot definitions and graphs1.05j Trigonometric identities: tan=sin/cos and sin^2+cos^2=11.05k Further identities: sec^2=1+tan^2 and cosec^2=1+cot^21.05o Trigonometric equations: solve in given intervals

2 Solve the equation \(\sec ^ { 2 } \theta \cot \theta = 8\) for \(0 < \theta < \pi\).

Question 2:
AnswerMarks Guidance
AnswerMarks Guidance
State \(\frac{1}{\cos^2\theta} \times \frac{\cos\theta}{\sin\theta} = 8\)B1 OE involving \(\sin\theta\) and \(\cos\theta\) only
Attempt use of \(\sin 2\theta\) identity to obtain \(\sin 2\theta = k\)M1
Obtain \(\sin 2\theta = \frac{1}{4}\)A1
Use correct process to find two values of \(\theta\) between 0 and \(\pi\)M1 Allow if working in degrees
Obtain 0.126 and 1.44A1 AWRT
Alternative: State \(\frac{1+\tan^2\theta}{\tan\theta} = 8\)B1
Attempt solution of 3-term quadratic equation to find values of \(\tan\theta\)M1 OE involving \(\tan\theta\) only
Obtain \(\tan\theta = \frac{8 \pm \sqrt{60}}{2}\)A1 OE
Solve \(\tan\theta = \ldots\) to find two values of \(\theta\) between 0 and \(\pi\)M1 Allow if working in degrees
Obtain 0.126 and 1.44A1 AWRT
## Question 2:

| Answer | Marks | Guidance |
|--------|-------|----------|
| State $\frac{1}{\cos^2\theta} \times \frac{\cos\theta}{\sin\theta} = 8$ | B1 | OE involving $\sin\theta$ and $\cos\theta$ only |
| Attempt use of $\sin 2\theta$ identity to obtain $\sin 2\theta = k$ | M1 | |
| Obtain $\sin 2\theta = \frac{1}{4}$ | A1 | |
| Use correct process to find two values of $\theta$ between 0 and $\pi$ | M1 | Allow if working in degrees |
| Obtain 0.126 and 1.44 | A1 | AWRT |
| **Alternative:** State $\frac{1+\tan^2\theta}{\tan\theta} = 8$ | B1 | |
| Attempt solution of 3-term quadratic equation to find values of $\tan\theta$ | M1 | OE involving $\tan\theta$ only |
| Obtain $\tan\theta = \frac{8 \pm \sqrt{60}}{2}$ | A1 | OE |
| Solve $\tan\theta = \ldots$ to find two values of $\theta$ between 0 and $\pi$ | M1 | Allow if working in degrees |
| Obtain 0.126 and 1.44 | A1 | AWRT |

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2 Solve the equation $\sec ^ { 2 } \theta \cot \theta = 8$ for $0 < \theta < \pi$.\\

\hfill \mbox{\textit{CAIE P2 2021 Q2 [5]}}