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

costheta.cos2theta.cos3theta=1/4

4cos6 theta cos4 theta cos2 theta=

Sum to n terms the series costheta-sin2theta-cos3theta+sin4theta+cos5theta-……

Solve: costheta+cos3theta+cos5theta+cos7theta=0

Find the sum of n terms the series: 1/(costheta+cos3theta)+1/(costheta+cos5theta)+1/(costheta+cos7theta)+…

Find the sum of the series costheta- (cos2theta)/(2!)+(cos3theta)/(3!)-… to oo

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

cos 3theta+cos 5theta+cos 7theta+cos 9theta=4 cos theta cos 2theta cos 6theta .

1+cos2 theta+cos4 theta+cos6 theta=

If cos theta+cos7 theta+cos3 theta+cos5 theta=0, then theta=