Question

FIND X
2+6+18+.............+x=531440

Answer 1

a=2; R=3

sum to nth term = a(R^n-1)/(R-1)

so

531440 = 2*(3^n-1)/(3-1)

= 3^n - 1

3^n = 531441

n = 12

x = 2x3^(12-1)=2x3^11

= 354294