Question

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Answer 1

listen one thing

formula used in this question are following.....

• $\cos {}^{2} ( \alpha ) - \sin {}^{2} ( \alpha ) = \cos(2 \alpha )$
• $1 + \cos(n \beta ) = 2 \cos {}^{2} ( \frac{n \beta }{2} )$
• $\cos( \alpha ) = \frac{b}{h}$
• now look at the answer.....