Question #6115f

1 Answer
Narad T.
Dec 23, 2016

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)

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