500
[this is true for some a's and x's] a = x [add a to both sides] a+a = a+x [a+a = 2a] 2a = a+x [subtract 2x from both sides] 2a-2x = a+x-2x [2a-2x = 2(a-x)] 2(a-x) = a+x-2x [x-2x = -x] 2(a-x) = a-x [divide both sides by a-x] 2 = 1
How/Why does 2 = 1?
It doesn't, at the last step you divide by zero which is undefined.
(a-x) = 0