OCR MEI C4 2007 June — Question 1 7 marks

Exam BoardOCR MEI
ModuleC4 (Core Mathematics 4)
Year2007
SessionJune
Marks7
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicHarmonic Form
TypeExpress and solve equation
DifficultyModerate -0.3 This is a standard harmonic form question requiring routine application of the R sin(θ - α) formula (finding R = √10 and α = arctan(3)) followed by solving a straightforward trigonometric equation. While it involves multiple steps, both parts are textbook exercises with no novel insight required, making it slightly easier than average.
Spec1.05n Harmonic form: a sin(x)+b cos(x) = R sin(x+alpha) etc1.05o Trigonometric equations: solve in given intervals

1 Express \(\sin \theta - 3 \cos \theta\) in the form \(R \sin ( \theta - \alpha )\), where \(R\) and \(\alpha\) are constants to be determined, and \(0 ^ { \circ } < \alpha < 90 ^ { \circ }\). Hence solve the equation \(\sin \theta - 3 \cos \theta = 1\) for \(0 ^ { \circ } \leqslant \theta \leqslant 360 ^ { \circ }\).

Question 1:
AnswerMarks Guidance
AnswerMarks Guidance
Point M: maximum point, \(y\) is maximum when \(\cos\theta = -1\), i.e. \(\theta = \pi\)M1 Finding \(\theta\) value
M is \((\pi a, 2a)\), \(\theta = \pi\)A1
Point N: \(y = 0\) when \(\cos\theta = 1\), i.e. \(\theta = 2\pi\)
N is \((2\pi a, 0)\), \(\theta = 2\pi\)A1 Both coordinates correct
# Question 1:

| Answer | Marks | Guidance |
|--------|-------|----------|
| Point M: maximum point, $y$ is maximum when $\cos\theta = -1$, i.e. $\theta = \pi$ | M1 | Finding $\theta$ value |
| M is $(\pi a, 2a)$, $\theta = \pi$ | A1 | |
| Point N: $y = 0$ when $\cos\theta = 1$, i.e. $\theta = 2\pi$ | | |
| N is $(2\pi a, 0)$, $\theta = 2\pi$ | A1 | Both coordinates correct |

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1 Express $\sin \theta - 3 \cos \theta$ in the form $R \sin ( \theta - \alpha )$, where $R$ and $\alpha$ are constants to be determined, and $0 ^ { \circ } < \alpha < 90 ^ { \circ }$.

Hence solve the equation $\sin \theta - 3 \cos \theta = 1$ for $0 ^ { \circ } \leqslant \theta \leqslant 360 ^ { \circ }$.

\hfill \mbox{\textit{OCR MEI C4 2007 Q1 [7]}}