SOLUTION: factor completely 7x^2-7x^2y-28x+28xy

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Question 571111: factor completely
7x^2-7x^2y-28x+28xy
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
We can find common factors in groups of terms, and see what we end up with:

If both factors in brackets were exactly the same, we would be finding a common factor again. We can fix that, because
%28-1%29%28-1%2By%29=%281-y%29
So

and we can write that in more elegant ways, and even factor out a -7
%28%28-1%297x%5E2%2B28x%29%28-1%2By%29=%28-7x%5E2%2B28x%29%28y-1%29=-7%28x%5E2-4%29%28y-1%29
Because x%5E2-4=%28x%2B2%29%28x-2%29, it can be factored too, to get to the full factorization.
-7%28x%5E2-4%29%28y-1%29=-7%28x%2B2%29%28x-2%29%28y-1%29