The 4th and 7th terms of a G.P. are and respectively. Find the sum of n terms of the G.P.

Nth term of GP is T_n = ar^{n - 1}

⇒ …(1)

Nth term of GP is T_n = ar^{n - 1}

⇒ …(2)

Divide (1) by (2)

⇒

⇒

⇒

Substituting in 1 we get

a = 1

Sum of GP for n terms =

a = 1, r = , n = n.

⇒

⇒

⇒