Question

Find the sum of the geometric sequence –3, 15, –75, 375, … when there are 7 terms and select the correct answer below.

Answer 1

-3, 15, -75, 375,…
  ×5  ×5   ×5

aⁿ = a₁rⁿ⁻¹
aⁿ = 3(5)ⁿ⁻¹

a₅ = -1875
a₆ = 9375
a₇ = -46875