zohal05lsa
zohal05lsa zohal05lsa
  • 25-09-2020
  • Mathematics
contestada

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

Respuesta :

mhanifa
mhanifa mhanifa
  • 25-09-2020

Answer:

  • 162

Step-by-step 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
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