Question

Boris is investigating a geometric series with an initial term of 5. Each successive term is – 3 times the previous term. What is the sum of the first 12 terms of this series?

Answer 1

Sum = 1328600

Explanation:

Givens

• r = -3
• n = 12
• a = 5

Equation

Sum = a(1 - r^n)/(1 - r)

Solution

• Sum = 5(1 - (-3)^12) / ( 1 - 3)
• Sum = 5(1 - 531441) / - 2
• Sum = 5(-531440) / - 2
• Sum = 1328600