Question

Find the sum of the first 9 terms of the arithmetic series given that f(n)=7n-17

Answer 1

• 162

Explanation:

Given AP

• f(n)=7n - 17
• S₉ = ?

Solution

Using formula Sₙ = 1/2n(f(1) + f(n))

• f(1) = 7*1- 17 = -10
• f(9) = 7*9 - 17 = 46
• S₉ = 1/2*9*(-10 + 46) = 162