Question

Find the sum of the first 14 terms for the sequence -2,10,-50,....

Answer 1

Explanation:

a=-2

r=10/-2=-5

`s_(14)=a(r^n-1)/(r-1) \\=-2((-5)^(14)-1)/(-5-1) \\ =(1)/(3)(5^(14)-1)\\=(6103515625-1)/(3)\\=(6103515624)/(3)\\=2034505208`