Question

Find the number of terms of the AP $121,117,113,\dots ,-3$ ?

Answer 1

Given

$121,117,\mathrm{113...},-3$

$a=121$

$d=117-121=-4$

$a_n=-3$

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

$-3=121+(n-1)(-4)$

$-3=121-4n+4$

$4n=128$

$n=\frac{128}{4}$

$n=32$