3.Trigonometrical Ratios, Functions and Identities
medium

यदि $cos A = {3\over 4} , $ तब $32\sin \left( {\frac{A}{2}} \right)\sin \left( {\frac{{5A}}{2}} \right) = $

A

$7$

B

$8$

C

$11$

D

इनमें से कोई नहीं

Solution

(c) $32\sin \frac{A}{2}\sin \frac{{5A}}{2} = 16(\cos 2A – \cos 3A)$ 

$ = 16(2{\cos ^2}A – 1 – 4{\cos ^3}A + 3\cos A)$ 

$ = 16\left( {2 \times \frac{9}{{16}} – 1 – 4 \times \frac{{27}}{{64}} + 3 \times \frac{3}{4}} \right) = 11$.

Standard 11
Mathematics

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