Question 189148
Once you solve for all x that 'work', you need to check those values to ensure they do not end up being an invalid answer.

For instance, if x = -1 or x=2 end up being solutions for this problem, then you can't use them. Both of those values result in a denominator that is 0. 

This applies to every problem. When you solve for roots, all you get are 'possible' answers. You always need to take a look at those possible answers to verify that they are, in fact, valid.

Another common place where a possible answer is invalid are problems that ask for the 'length' of something. Many times, the possible solutions will include at least one negative value. Since a 'length' can't be negative, those answers are invalid too. 

Hope that helps