Given a, b, and c and their squares, find ab, ac, and bc.

I'm not sure how to start this. I'm allowed to add a, b, and c to each other (including subtraction since that's just opposite addition) but I don't know how to use what I have to find what I need. I'm bad at conceptual things like this with no actual numbers. Any help is appreciated, thanks!

(a+b+c)^2 = a^2 + 2ab + 2ac + b^2 + 2bc + c^2