Question

if the sum of 3rd term of GP is 3 and 6th term is 81 find the sum of first 6 term​

Answer 1

Answer:

Let a & r be the first term & common ratio of given G.P. then according to given conditions

ar2=12(1)

ar5=96(2)

dividing (2) by (1),

ar5ar2=9612

r3=8⟹r=2,a=3

hence, the sum of first 9 terms

S9=a(r9−1)r−1

=3(29−1)2−1

=3(512−1)1

=1533