Question

Find the sum of last 8 terms of the A.P. –12, –10, –8, ……, 58.

Answer 1

First we will reverse the given A.P. as we have to find the sum of last 8 terms of the A.P.

58, …., –8, –10, –12.

Here a = 58, d = –2

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

`=> S_8 = 8/2 [2 xx 58 + (8 -1)(-2)]`

= 4(116 – 14)

= 4 × 102

= 408

Therefore the sum of last 8 terms of the A.P. –12, –10, –8, ……, 58 is 408.