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 "x-1" 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/(x-1) -  (1-2x)/x

i've looked through my notes and have no examples that quite match that i can follow to get through it. please help!




Hi Simone,

You know that with numerical fractions you can always find a common denominator by multiplying the denominators. For example if you have

1/8 - 5/12

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

x(x - 1)



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