Does anyone know any good websites or information on dummy variables in algebra. Let me explain what i mean by dummy variable, what i mean is a pro-numeral that one inserts into an algebraic expression such that the expression stays the same but such that you can factorize it neatly. For example if i have x2 + 6x. If i add a dummy variable, it might factorize more elegantly. I decide to use 9 x2 + 6x + 9 - 9 I have to minus the nine as well to keep the original expression the same. I shall factorize the first 3 terms, it becomes (x + 3)2 - 9 9 is 32 (x + 3)2 - 32 Using the difference of 2 squares (x + 3 - 3)(x + 3 + 3) = x(x + 6) So this is the long way, but some times you cant factorize an expression and using a dummy variable helps. You cant factorize a4 + 4b4 with out a dummy variable So back to my question, does any one know of any webs sites or stuff that has more info or exercises on dummy variables in algebra?