Find the 10th term in an AP where the first term is 3 and whose 1st, 4th and 13th terms form a GP.

Answer 1

a = 3

Since the GP has a common ratio

(a+3d)/(a) = (a+12d)/(a+3d)
(3+3d)/3 = (3+12d)/(3+3d)
1+d = (1+4d)/(1+d)
d = 2

a+9d = 3+9*2 = 21