Question

In an AP, the first term is 22, nth terms is -11 and sum of first n terms is 66. Find the n and hence find the 4 common difference.

Answer 1

Here, a = 22, T_n = -11 and S_n = 66

Let d be the common difference of the given AP.

Then, T_n = -11

\(\Rightarrow\) a + (n - 1)d d = 22 + (n - 1) d = -11

\(\Rightarrow\) (n - 1) d = -33    .......(i)

The sum of n terms of an AP is given by

Thus, n = 12 and d = -3