The cardinal sin of algebra! When you divide both sides of the equation by x, you're essentially telling x=0 to get lost from the party! But that sneaky solution was there all along! See, when you factor out 3x from that cubic equation, you're basically saying "Hey x, I don't care if you're zero!" Then you solve the quadratic like a boss, finding x=-1 and x=-3, while x=0 sits in the corner plotting its revenge. Every math teacher watching this: *hyperventilates in polynomial*