I am doing online homework at CourseCompass.com and got a problem that I cannot figure out. Maybe somebody here can help me?

Use the difference of two squares formula to factor the polynomial.

49 - (x+7)²

I got as far as [7 + (x+7)] [ 7 - (x+7)] but I do not know what to do from here.

The site says the answer is -x(x+14) but I have no idea how they came to that. Ideas?