Question

I've tried to get the answer for this 13 times now (not joking), plzzz help: write a formula that represents the number of people in the nth row (pre-calc problem, I only need the formula)

I will report if sent a link

Answer 1

• 2820 seats
• aₙ = 3n + 9

Explanation:

This is an AP with:

• The first term a₁ = 12
• Common difference d = 3
• Number of terms n = 40

Number of the seats:

• Sₙ = 1/2*n(a₁ + aₙ) = 1/2n(2a₁ + (n - 1)d)
• S₄₀ = 1/2*40(12*2 + 39*3) = 2820 seats

Formula of nth term:

• aₙ = a₁ + (n - 1)d
• aₙ = 12 + (n - 1)*3 = 12 + 3n - 3 = 3n + 9
• aₙ = 3n + 9