Find the sum to n terms of the following series:
`cos alpha + cos (pi - alpha) + cos (2pi + alpha) + .......(0 < alpha < (pi)/2)`.

Find the sum to n terms o the series cos^2 alpha+cos^2(alpha+beta)+cos^2(alpha+2beta)+..

Find the sum to n terms o the series cos^2 alpha+cos^2(alpha+beta)+cos^2(alpha+2beta)+..

(cos alpha + (cos ((2 pi) / (3) + alpha)) + cos ((4 pi) / (3) + alpha))

Sum the series : (1+cos alpha) +(1+ cos2alpha) +(1+ cos3alpha) +..... to n terms.

Find the sum of the series cosalpha+x cos(alpha+beta)+ x^2/(2!)cos(alpha+2beta)+…to oo

Find the sum of the series cosalpha+x cos(alpha+beta)+ x^2/(2!)cos(alpha+2beta)+…to oo

Find the sum of the series cos^(3)alpha+cos^(3)2 alpha+...... to n terms

If a_(1),alpha_(2)...,alpha_(n) are in A.P.with common difference d,then the sum of the series,sin d[cos ec alpha_(1)cos ec alpha_(2)+cos ec alpha_(2)cos ec alpha_(3)+...+...+cos ec alpha_(n-1)cos ec alpha_(n) is:

If x cos alpha = y cos ( 2pi//3+ alpha ) = z cos ( 4pi//3+ alpha ) , " then " xy+yz+zx=

If 0