Question

In an A.P. the first term is 25, n^th term is –17 and the sum of n terms is 132. Find n and the common difference.

Answer 1

First term a = 25

n^th term = –17

`=>` Last term l = –17

Sum of n terms = 132

`=> n/2 [a + l] = 132`

`=>` n(25 – 17) = 264

`=>` n × 8 = 264

`=>` n = 33

Now, l = –17

`=>` a + (n – 1)d = –17

`=>` 25 + 32d = –17

`=>` 32d = – 42

`=> d = -42/32`

`=> d = -21/16`