Question

What is the sum of a 30–term arithmetic sequence where the first term is 72 and the last term is –102?

Answer 1

Let n = 30, a = 72 and l = -102. Then using the formula for the arithmetic progression,
\[S = n(a + l)/2 = 30[72 + (-102)]/2=-450.\]

Answer 2

oh sorry, i mean it is for the sum of an AP.
still the answer is the same.

Answer 3

you are right hehe