Question

Please solve the sum!! ​

Answer 1

Step-by-step explanation:

Hey ❤

Please refer to the attachment ✌❤

Answer 2

SOLUTION

L.H.S

$= > cos2x.cos \frac{x}{2} - cos3x \: cos \frac{9x}{2} \\ = now \\ = > after \: dividing \: and \: multipliying \: it \: with \: 2 \: we \: get \\ \\ = > \frac{1}{2} (2cos2x \: cos \frac{x}{2} - 2cos3x \: cos \frac{9x}{2} ) \\ = as \\ = > 2cosx \: cosy = cos(x + y) + cos(x - y) \\ so \\ = > \frac{1}{2} cos(2x + \frac{x}{2}) + cos(2x - \frac{x}{2} ) - cos(3x + \frac{9x}{2} ) - cos(3x - \frac{9x}{2} \\ \\ = > \frac{1}{2} (cos \frac{5x}{2} + cos \frac{3x}{2} - cos \frac{15}{2} - cos \frac{3x}{2} ) \\ \\ = > \frac{1}{2} (cos \frac{5x}{2} - cos \frac{15x}{2} ) \\ \\ = > \frac{1}{2} ( - 2sin \: 5x. - sin \frac{5x}{2} ) \\ \\ = > sin5x.sin \frac{5x}{2} .......rhs$

hope it helps ✔️☺️