X^2-4 / x^2+5x+6 = 0
The answer is 2.
Then it says , "Solving this for x gives either 2 or −2. That means either of these values will make our numerator equal zero."
... I don't know why those values makes the numerator equal to zero.
It also says,"Any values that make our denominator zero must be rejected."
(Which has to do with the next step)
x=-3 ; x=-2
"This means that if x is −3 or −2, we end up dividing by zero. That means that −2 cannot be a valid solution, leaving 2 as the only valid answer."
My question is, how do you know if you're dividing by zero or the values given will make the numerator equal zero?