Answer:
see explanation
Step-by-step 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
