Question

The least value of 'a' such that $(a-1)x^2+4x+a+5>0\forall x\in R,a\in N$ is

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

Answer: (B)

$(a-1)>0$ and $D<0$
$D<0$
$\Rightarrow 16-4(a-1)(a+5)<0$
$\Rightarrow a^2+4a-9>0$
$\Rightarrow a\in (-2+\sqrt{13,\infty })$