Question

Find S8 for the series -2 + -10 + -50 + -250 +...

Answer 1

39062.5

Explanation:

-2+-10+-50+-250

-10/2=-250/-50 = 5

sum of the geometric sequence

Sₙ = arⁿ⁻¹ /r-1 a=-2, r = 5

S₈ = -2(5)⁸⁻¹/(5-1) = 2(5⁷)/4 = 2(78125)/4= 78125/2= 39062.5

S₈=39062.5