The square of A+B = a 2+2ab+b 2

The square of A-B = a 2-2ab+b 2.

a^2+2ab+b^2+a^2-2ab+b^2=2(a^2+b^2)

That is 2+7 = 9 9/2 = the square of a+the square of b =4.5.

A^2+2AB+B^2-A^2-2AB+B^2=2AB

That is 7-2=5 5/2=AB=2.5.