Question

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

Answer 1

• 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