Question

Question #81cb8

Answer 1

= 2sin x.sin 2x

Explanation:

Use trig identity:
`cos a - cos b = - 2sin ((a + b)/2)sin ((a - b)/2)`
In this case -->
:
`cos x - cos 3x = - 2sin (- x).sin 2x = 2sin x.sin 2x`