How do you find the sum of the first 10 terms of the arithmetic sequence, if the first term is 5 and the common difference is -8?

1 Answer
Nov 9, 2016

S_10 =-310

Explanation:

There is a formula for the sum of n terms of an A.P.

S_n = n/2[2a + d(n-1)]

FRom the information given, we know that:

n = 10 " " a= 5, " "d = -8" " substitute the values

S_10 =10/2[2(5)-8((10)-1)]

S_10 = 5[10-80+8]

S-10 = 5 xx-62 = -310