Let (aₙ) be the sequence defined by the recursive relation aₙ = aₙ₋₁ + 4n + 1, with initial term a₀ = 0. Use iteration to find a closed formula for the sequence. Simplify your answer.
a) aₙ = 2n² + 3n
b) aₙ = n² + n
c) aₙ = 4n² + 5n
d) aₙ = 3n² + 2n