S(n) = (x(1) + x(n))/2 * n
x(n) = x(1) + d(n - 1)
n = 33
x(17) = 28
S(n) = (x(1) + x(33))/2 * 33
x(1) + x(33) = x(1) + (x(1) + 32d) = 2*(x(1) + 16d) = 2*x(17)
S(n) = (x(1) + x(33))/2 * 33 = x(17)*33 = 28*33 = 924
S(n) = (x(1) + x(n))/2 * n
x(n) = x(1) + d(n - 1)
n = 33
x(17) = 28
S(n) = (x(1) + x(33))/2 * 33
x(1) + x(33) = x(1) + (x(1) + 32d) = 2*(x(1) + 16d) = 2*x(17)
S(n) = (x(1) + x(33))/2 * 33 = x(17)*33 = 28*33 = 924