Question

If the equation $9x^2+6kx+4=0$ has equal roots, then find the value of k.

• A. zero
• B. either 2 or zero
• C. either –2 or zero
• D. either 2 or –2

Answer 1

The correct option is D

either 2 or –2

Step 1:- For, $9x^2+6kx+4=0$, $\Rightarrow a=9,b=6k,c=4$

Value of discriminant $D=36k^2–4\left(4\right)\left(9\right)$ [D = $b^2-4ac$]

$D=36k^2–4\left(36\right)$

Step 2:- The roots of quadratic equation are real and equal when $D=0$

Step 3:- $36k^2–4\left(36\right)=0$

$\Rightarrow k^2=4$

$\Rightarrow k=-2or2$