I'm currently reviewing pre-calculus material and encountered a little problem with an absolute value expression. |3-x|=x-3 Now the way I learned absolute value expressions was that there's a positive and a negative case. So I got: 3-x=x-3 x=3 and -(3-x)=x-3 gives 0=0. Stupid question, but isn't 0=0 in general valid for all values of x? And I don't understand how you get to the solution x≥3.