a₁ = 9
a₂ = 9+2 → a₂ = a₁ + 2. Since it's an AP, d, the common difference is 2
1) Then the recursive formula is :
a(n) = a(n-1) + 2
2) Explicit formula:
It's an AP, with first term a₁, d= common difference and n = number of term, which is the number of rows in this problem.
the value of the nth term is given by the formula is:
value of nth term = a₁ + (n-1).d
3) Number of seats in the 12th row:
9 + (12-1).2 = 31 seats
