Question

The equation $9x^2+3kx+4=0$ has repeated roots, when $k$ is equal to

• A. $\pm 1$
• B. $\pm 2$
• C. $\pm 3$
• D. $\pm 4$

Answer 1

The correct option is D $\pm 4$

A quadratic equation $a{x}^2+bx+c=0$ has discriminant $D=b^2-4ac$

As per concept of nature of roots, for repeated roots, $D=b^2-4ac=0$
Here, $a=9,b=3k,c=4$
$\therefore (3k{)}^2-4\times 9\times 4=0$
$⟹9k^2=4\times 9\times 4$

$⟹k=\pm 4$