Question

Question #6115f

Answer 1

The answer is `=9/2(costheta-cos5theta)`

Explanation:

We use

`cos(a-b)=cosacosb+sinasinb`

`cos(a+b)=cosacosb-sinasinb`

We substract the 2 equations

`cos(a-b)-cos(a+b)=2sinasinb`

Here,

`a=3theta`

and `b=2theta`

`:.9sin3thetasin2theta=9/2(cos(3theta-2theta)-cos(3theta+2theta))`

`=9/2(costheta-cos5theta)`