Question

The algebraic expression of the SUM is n²+2n. What is the common difference and first term

Answer 1

see explanation

Explanation:

substitute n = 1, 2 into the sum rule

1² + 2(1) = 1 + 2 = 3 , then

a₁ = 3

2² + 2(2) = 4 + 4 = 8 , then

a₁ + a₂ = 8

3 + a₂ = 8 ( subtract 3 from both sides )

a₂ = 5

then

common difference d = a₂ - a₁ = 5 - 3 = 2

First term is 3 and common difference = 2