Simplify $\frac{x^3-x}{x^2+xy+x+y}$ $$\frac{x^3-x}{x^2+xy+x+y}$$
What I did:
 $$\frac{x}{xy+x+y}$$
through simplifying the $x$'s.
But it's not right.  
What did I do wrong?

Notice that $$\frac{x^3-x}{x^2+xy+x+y} = \frac{(x+1)(x^2-x)}{(x+1)(x+y)} =\frac{x^2-x}{x+y}$$
P.S.: You cannot simplify the $x$'s  without considering all terms of the numerator and the denominator.
