In any quadratic ax² + bx + c, we can split the bx term up into two new terms which we want to equal the product of a and c. In this case, we have x² + 0x - 9. (the 0x is a placeholder) We want two numbers that add to 0 and multiply to get -9. Obviously, these numbers are 3 and -3.
Now we have 3(x² + 3x - 3x - 9). Let's factor. 3(x(x+3)-3(x+3)) <u>3(x-3)(x+3)</u>
There are multiple shortcuts which you could make here, FYI: Instead of splitting the middle, if your a value is 1, you can go straight to that step (x+number)(x+other number). Whenever you have a difference of squares, like a²-b², that factors to (a+b)(a-b).