Q: Factor this: -3x² + 12x – 12
A: Before I start factoring, I look to see if there is any number that I can “pull out” (this is techinically called the “greatest common factor method”). See how each number is divisible by 3? So, I can pull a 3 out…. But, I even like to pull the – out too, so I will pull out a -3 like so:
-3x² + 12x – 12 = -3 (x² – 4x + 3)
So, now we have this: -3 (x² – 4x + 3)
Now, we ask ourselves: What two numbers multiply to give +3 and combine to get -4. The answer is -1 and -3… -1*-3 = 3 and -1 + -3 = -4.
So, we can factor like so:
-3 (x² – 4x + 3) = -3(x – 1)(x – 3)
You can FOIL that back out to make sure it worked!