`costheta.cos2theta.cos3theta=1/4`

costheta-cos2theta=sin3theta

cos theta cos2 theta cos3 theta=(1)/(4)

Find the sum of the series costheta.cos2theta+cos3theta.cos4theta+cos5theta.cos6theta+…to n terms

Find the sum of the series costheta.cos2theta+cos3theta.cos4theta+cos5theta.cos6theta+…to n terms

if 13theta=pi ,then show that cos3theta+cos5theta+2costheta.cos9theta=0

Prove that (sin theta+ sin 2theta + sin 3 theta)/(costheta+cos2theta+cos3theta)=tan 2 theta

If sintheta+sin2theta+sin3theta=sinalpha and costheta+cos2theta+cos3theta=cosalpha , then theta is equal to

4costheta cos 2theta cos3theta - 2cos 4theta=1

costheta+cos2theta+cos3theta+.......+cos(n-1)theta+cosntheta=

Prove that: cos2theta.costheta/2-cos3theta.cos(9theta)/(2)=sin5theta.sin(5theta)/(2)