Question

find the sum of first n terms of G.P .3,9,27,81,243,...​

Answer 1

Answer:

3 + 9 + 27 + 81 + 243 + 729 + 2187 + 6561

Formula used:

a{(rn - 1)/(r - 1)}, a is first term, r is common ratio, n is number of terms

Calculations:

31 + 32 + 33 + 34 + 35 + 36 + 37 + 38

a = 3, r = 3, n = 8.

a{(rn - 1)/(r - 1)}

⇒ 3 × {(38 - 1)/(3 - 1)}

⇒ 9840