In an AP:
Given $l = 28, S = 144$, and there are total 9 terms. Find $a$.

Given:

In an A.P., $l = 28, S = 144$, and there are total 9 terms.

To do:

We have to find $a$.

Solution:

$a_n=l=28$

We know that,

$\mathrm{S}_{n}=\frac{n}{2}[a+l]$

$S_n=\frac{9}{2}[a+28]$

$144(2)=9(a+28)$

$16(2)=a+28$

$a=32-28$

$a=4$

Therefore, $a=4$.