Asked by leonard

The third,fourth and eight term of A.P form first three consecutive term of G.P.if the sum of the first ten term of A.P is 85.calculate the first term of both A.P and G.P,common ratio
Answered by oobleck
(a+3d)/(a+2d) = (a+7d)/(a+3d)
10/2 (2a+9d) = 85
solve to get
a = -5, d=3
so the AP is
-5, -2, 1, 4, 7, 10, 13, 16, 19, 22, ...
and the GP is
1, 4, 16, ...
making r=4