Question

Which term of the $AP.$ $135,131,127,...$ is its first negative term?

Answer 1

$135,131,\mathrm{127....}$

nth term of an AP$=a+(n-1)d$

Here $a=135$

$d=131-135=-4$

$135+(n-1)(-4)<0$

$135<4n-4$

$4n>139$

$n>34.75$

$\therefore n=35$

$a_{35}=a+34d$

$=135+34(-4)$

$=135-136=-1$

$\therefore {35}^{th}$ term is its first negative term