Question

For the sequence $72,70,68,66,.......$ write the value of $n$ for $a_n=40$.

Answer 1

Given series is $72,70,68,66,.......$

$d=70-72=-2$

Let $a_n=40$
$a_n=a+(n-1)d$
$\Rightarrow 40=72+(n-1)2$
$\Rightarrow 40-72=-2n+2$
$\Rightarrow -32=-2n+2$
$\Rightarrow -34=-2n$
$\Rightarrow n=17$
$\therefore {17}^{th}$ term is $40$