How do I find the lcd from say x-4 and x+2 (those are the denominators). Is there any rule that always works?? Can¨'t figure out this by myself.. Thanks

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- Apr 15th 2009, 11:11 AMstrunzchoosing lowest common denominator
How do I find the lcd from say x-4 and x+2 (those are the denominators). Is there any rule that always works?? Can¨'t figure out this by myself.. Thanks

- Apr 15th 2009, 11:30 AMmasters
Hi strunz,

In your situation, the LCD is (x - 4)(x + 2). If you're having trouble with LCDs in general, see this lesson:

Adding and Subtracting Rational Expressions - Apr 15th 2009, 03:11 PMLinaD3
I would say just multiple both of the denominators to get the lcd.

- Apr 15th 2009, 03:15 PMicemanfan
In general, you have to determine if the denominators have any common factors. For instance, the lowest common denominator in the example

is because the two fractions' denominators share the common factor of x + 3. If the denominators share no common factors, then the lowest common denominator is the product of each of the individual denominators.