Q. The least value of 'a' such that $(a-1) x^2+4 x+a+5>0 \forall x \in R, a \in N$ is
Complex Numbers and Quadratic Equations
Solution:
$(a - 1) > 0$ and $D < 0$
$D < 0$
$\Rightarrow 16-4(a-1)(a+5)<0 $
$\Rightarrow a^2+4 a-9>0$
$\Rightarrow a \in(-2+\sqrt{13, \infty}) $
