$$X^2-49=0$$
$$X^2=49$$
$$\sqrt{X}= ± \sqrt{49}$$
$$X=±7$$
Discriminant: $$B^2-4ac$$
$$A=1$$
$$B=0$$
$$C=49$$
$$(0)^2-4(1)(49)$$ $$0-196=(-196)$$
A negative discriminant means that the roots of the equation is not real, but as I have shown, the solution is clearly $±7$ which are both real and equal, and would mean that the discriminant should be equal to 0 as well.
Please help me. And God Bless