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

Find the sum of the series 1+cos^2theta+cos^2thetacos2theta+cos^3 theta cos3theta+… to oo

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

Solve: costheta+cos3theta+cos5theta+cos7theta=0

Solve: cos5theta=cos2theta

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

Solve cos theta+cos 2theta+cos 3theta=0 .

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

Solve cos theta+cos 7 theta+cos 3theta+cos 5 theta=0 ,

Prove that: (sin2theta)/(costheta cos3theta)+(sin4theta)/(cos3theta.cos5theta)+(sin6theta)/(cos5theta.cos7theta)+… to terms = 1/(2sintheta) [sec(2n+1)theta-sectheta]