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

$\displaystyle \frac{2}{(x + 3)(x - 8)}, \frac{5}{(x + 2)(x + 3)}$ is $\displaystyle (x + 3)(x + 2)(x - 8)$ 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.