Asked by Angel

Find the sum of the first 60 terms of the arithmetic sequence whose first term is −15 and whose common difference is 3.

I really need help! please can someone help me I need this asap!!
Answered by oobleck
just use your formula
S60 = 60/2 (2a + 59d)
Answered by R_scott
the 60th term is ... -15 + (3 * 59) = 162

the sum of the terms is
... the average of the first and last terms ... (-15 + 162) / 2
... multiplied by the number of terms ... 60