Question

Find the first term of an A.P whose common difference is $-3$ and $n=18$, $n^{th}$ term is $-5$

Answer 1

$a_n=-5,n=18,d=-3$

$\Rightarrow T_n=a+(n-1).\left(d\right)$

$\Rightarrow -5=a+17.(-3)$

$\Rightarrow -5=a-51\Rightarrow a=51-5=46$.