Find the sum: `costheta+ (a cos2theta)/(1!)+(a^2cos3theta)/(2!)+(a^3cos4theta)/(3!)+…to oo`

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

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

Solve: cos3theta+2costheta=0

Solve that equation : costheta+cos3theta-2cos2theta=0

Solve that equation : costheta+cos3theta-2cos2theta=0

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

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

1 + (cos 2 theta + cos 6 theta)/(cos 4 theta) = (sin 3 theta)/(sin theta).

Solve the following equation: costheta\ cos2theta\ cos3theta=1/4

If (a cos theta_(1), a sin theta_(1)), ( a cos theta_(2), a sin theta_(2)), (a costheta_(3), a sin theta_(3)) represents the vertices of an equilateral triangle inscribed in x^(2) + y^(2) = a^(2) , then