Question

Find the 20th term of the progression.
$-12,-5,2,9,16,23,30,....$

Answer 1

Let $-12,-5,2,9,16,23,\mathrm{30....}$

Here $-5+12=7$

$2+5=7$

$9-2=7$

$\therefore d=7$

$\therefore$ given sequence is in $AP$ with $a=-12,d=7andn=20$

$nth$ term of the $AP$ is given by

$a_n=a+(n-1)d$

$a_{20}=a+(20-1)d$

$=a+19d$

$=-12+19\left(7\right)$

$=-12+133$

$a_{20}=121$