Question

Find the sum of first 22 terms of the A.P. : 1, 4, 7, 10,.......
Here $a=1$

Answer 1

Given,

$a=1$

$d=4-1=3$

$S_n=\frac{n}{2}[2a+(n-1\left)d\right]$

$S_{22}=\frac{22}{2}\left[2\right(1)+(22-1\left)3\right]$

$=715$