Question

The value of k for which the quadratic equation $x^2+4kx+4=0$ has equal roots is/are ____.

• A. $\pm 2$
• B. $\pm 1$
• C. $\pm 4$
• D. $\pm 9$

Answer 1

The correct option is B $\pm 1$

A quadratic equation has equal roots when discriminant, D = 0.

Givent that $x^2+4kx+4=0$ has equal roots.

$\therefore D=0$
$\Rightarrow b^2-4ac=0$
$\Rightarrow b^2=4ac$

Here, $a=1,b=4k$ and $c=4$

$\Rightarrow (4k{)}^2=4(1\left)\right(4)$
$\Rightarrow 16k^2=16$
$\Rightarrow k=\pm 1$