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.