Question

find the sum of the ap; 2+6+18+54+...................+1458

Answer 1

Looks like a GP, with a = 2 and r = 3
Which term number is 1458 ?
ar^(n-1) = 1458
2(3^(n-1)) = 1458
3^(n-1) = 729 , but I know 3^6 = 729
so n-1 = 6 and n = 7

so now you want sum(7) = 2(3^7 - 1)/(3-1) = ...