Question

Find the value of k for which the quadratic equation $x^2–4x+k=0$ has real and equal roots.

• A. 0
• B. -2
• C. 4
• D. -4

Answer 1

The correct option is C

4

On comparing $x^2–4x+k=0$ with standard form $a{x}^2+bx+c=0$, we get

$a=1,b=-4,c=k$

The roots of quadratic equation are real and equal only when discriminant, $D=0$.

$D=\sqrt{b^2-4ac}=4^2–4k=16-4k$

$\Rightarrow 16-4k=0$

$\Rightarrow k=4$