- Home
- Standard 11
- Mathematics
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