Question

If the sum of the 3rd term and 5th term of a g.p is-60 and the sum of the 5th term and 7th term is-240 find the common ratio, the first term, sum of the 8th terms

Answer 1

a+2d + a+4d = -60

a+4d + a+6d = -240
solve for a and d as usual, then you want
S8 = 8/2 (2a+7d)