Question

x+y=x-5
I want to get y alone on one side, so if I subtract x from both sides, what would be x - x?

Answer 1

x-x=0, so y = -5

whatever value x has, the equation is still true. You cannot solve for y in terms of x, because y is independent of x in this case.

If you have 3=3, then x+3 = x+3 whatever x is.

Here, y = -5, so x+y = x-5 whatever x is.