What is y=x^2-8x+12i don't have a graphing calc at home

First u have to find 2 numbers that add to give - 8 and multiply to give 12.
So the 2 numbers will be - 2 and - 6
Put them in your equation:

Now split this from the middle and into 2 brackets to get :
x (x-2) and -6 (x-2)

You can check if they're correct by expanding the them. Also, another way of checking would be to make sure that the numbers inside the brackets on both sides are the same.

Last step is to just split them into 2 separate brackets:
(x-2) (x-6)

I've put a picture of how the graph for this would look.
By the way, if you don't have a graphing calculator, you should download the app "photomaths" it's really simple and gives u graph solutions too. :)