Find the Sum of Cosine series when angle are in AP

Find the Sum of sine series when angle are in AP

If first term is 8 and last term is 20 common difffence is 2. find the value of n when the series are in AP.

Problem on Trigonometric Series in Which angle are in A.P.

Problem on Trigonometric Series in Which angle are in A.P.

The sum of the third and the seventh term of an A.P. is 6 and their product is 8. Find the sum of first sixteen terms of an A.P.

Trigonometric Series in Which angle are in A.P.

Trigonometric Series in Which angle are in A.P.

Trigonometric Series in Which angle are in A.P.

Trigonometric Series in Which angle are in A.P.

Find the sum to n terms of a series is 7n^2-5n . Show that it is an AP and find the 15^th term.