Question

Which term of the AP: $31,28,25,........$ is the first negative term.

Answer 1

AP$=31,28,25,....$

$a=31$ & $d=-3$

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

$0=31+(n-1)(-3)$

$\Rightarrow -31=(n-1)(-3)$

$\Rightarrow n=\frac{31}{3}+1=\frac{34}{3}=11.33$

So ${12}^{th}$ term is the first negative term.