hi, i'm totally lost. i understand that you need to find a lowest common denominator to subtract two fractions (rational expressions) with different denominators. but what if the denominators are "x1" and "x". is x the common denominator? if so what happens to the "1"? do you know of any live online help i can get with the following: 3/(x1)  (12x)/x i've looked through my notes and have no examples that quite match that i can follow to get through it. please help! thanks, 

Hi Simone, You know that with numerical fractions you can always find a common denominator by multiplying the denominators. For example if you have
then 12 8 = 72 is a common denominator, even though it is not the lowest common denominator. The same is true for rational expressions, if you multiply the denominators you will have a common denominator. In your example a common denominator is
Penny 

