# Math Help - Plugging in number

1. ## Plugging in number

my teacher for our first homework assignment gave us half answers, but i cant get the correct answer for this:

$(x^2 - 14x - 51)/(x^2 - 4x - 21)$ when you plug in -3 is equal to what?

my math teacher says 2 is the answer, but i always get $(9 + 42 - 51) / (9+12 -21) = (51-51) / (21-21) = 0/0$

is my math teacher wrong? or what am i doing incorrectly?

2. This simply means that the function is not defined at the point x=-3. So if you're asked what is f(-3) just answer it doesn't exist or it is not defined.