Quite silly, you are subtracting the number from a slightly modified version of that number, intuitive that it could cancel out, hardly a trick. I guess the 'trick' is sticking a bunch of 2's in there that cancel out to hide the fact that you're doing a mere addition to the original number
((x + 5)*2 - 2)/2 - x = ((x + 5) - 1) - x = x + 4 - x = 4