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Please help I don't know how to do this ​
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Please help I don't know how to do this ​

Please help I don't know how to do this ​-example-1
User Edan Chetrit
by
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1 Answer

4 votes

Answer:

  • 18

Explanation:

Given AP with:

  • a₁= 28, aₙ = 79, Sₙ = 963

Use the formula:

  • Sₙ = 1/2n(a₁ + aₙ), sum of the first n terms

Substitute given values and solve for n:

  • 963 = 1/2n(28 + 79)
  • 963 = 1/2n(107)
  • 1/2n = 963/107
  • 1/2n = 9
  • n = 9*2
  • n = 18

User Fred Strauss
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