SRJC P1 Q7

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Timothy Gan

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SRJC P1 Q7
Timothy Gan
SRJC P1 Q7

Let $\text{f}\left( r \right)=\frac{\sin \left[ (2r+1)\theta \right]}{\cos \theta },r\in {{\mathbb{Z}}^{+}}$.

(i)

Show that $\text{f}\left( r \right)-\text{f}\left( r-1 \right)=A\cos \left( Br\theta \right)\tan \left( \theta \right)$, where $A$ and $B$ are to be determined.

(ii)

By using the result part (i), show that

$\cos 2\theta +\cos 4\theta +…+\cos 2N\theta =\frac{1}{2}\left[ \frac{\sin \left[ \left( 2N+1 \right)\theta \right]}{\sin \theta }-1 \right]$ .

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Published: 31st March 2023
SRJC P1 Q7
Written by
Timothy Gan
This is Tim. Tim loves to teach math. Tim seeks to improve his teaching incessantly! Help Tim by telling him how he can do better.
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Published: 31st March 2023

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