what is the sum of an 8-term geometric series if the first term is -11, the last term is 859,375 and the common ratio is -5?

Answer 1

S_n = a₁(1 - rⁿ) / (1 - r)

S₈ = -11(1 - (-5)⁸) / (1 + 5)

S₈ = -11(1 - 390625) / 6

S₈ = -11( -39624) / 6

S₈ = 435864 / 6

S₈ = 72,644