Question

Which of the following correctly uses the formula for the finite geometric series to derive the sum of the first seven terms of the geometric series 14 + 21 + 31.5 + 47.25 + . . . ?(1 point)

S7=14−14(1.5)71−1.5


S7=14−14(1.5)71+1.5


S7=14−14(1.5)61−1.5


S7=14−14(7)71−7

Answer 1

Use S_n = a(1 − r^n)/(1 − r). Here a = 14 and r = 1.5, so

S7 = 14(1 − (1.5)^7)/(1 − 1.5),

which is the first option.