30 and 13
x-y=17 and x+y=43
x=17+y and x=43-y, so 17+y=43-y
so y=13
43-13=30, so x=30 and y=13
Yes they are equivalent expressions. If you take the z to the power of two, and subtract that from the other z to the power of two, it is zero. So you are left with four which is the answer
