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

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

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

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

Solve: costheta+cos3theta+cos5theta+cos7theta=0

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

Solve: cos3theta+2costheta=0

Solve: cos3theta+costheta=0

Prove: (sintheta)/(1-costheta)=cos e c\ theta+cottheta

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

Prove that, 1/(costheta-cos3theta)+1/(costheta-cos5theta)+1/(costheta-cos7theta)+…+to n terms = 1/(2sintheta) [cottheta-cot(n+1)theta]