Question

Which values will only have one zero??

Answer 1

If it has a single zero that means it has to be just touching the x-axis with its tip.

We know that if it has only one zero, the discriminant equals 0.

So,

$D=b^2-4ac=0\implies (-k)^2-4(1)(9)=0$

Solving for k,

$k=\pm\sqrt{36}=\boxed{\pm{6}}$.

Hope this helps.