So far your response is the only one that has mentioned undefined expressions. You are right that it is important to look for a denominator of 0.

So far your response is the only one that has mentioned undefined expressions. You are right that it is important to look for a denominator of 0. A denominator of 0 means the expression is undefined and then it cannot be used for much of anything. (Except in instances like last weeks worksheet when we were trying to determine how many batches of tile would equate to 0 profit.) I usually get to distracted in the problem to notice a 0 denominator until I am at the last step. However, I have noticed that if you look at the denominator before working the problem you can tell what number will not work. For example: x²=6/x-5. We know that if we use x=5 then the denominator will become 0 and cancel out before working through the problem. Thanks for reminding us how important this is!