What is the value of $a-b$ when $a$ and $b$ are constants

Question

The expression $x^2-k^2$ where $k$ is a constant is equivalent to the expression $(x+a)(x-b)$ where $a$ and $b$ are constants. What is the value of $a-b$?

Answer 1

Hint

$$x^2 -k^2 = x^2 + 0x - k^2$$

Can you take this from here? Also take note of fourRightRotation's hint.