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Math Help - choosing lowest common denominator

  1. #1
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    choosing 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?? CanĘ't figure out this by myself.. Thanks
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  2. #2
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    Quote Originally Posted by strunz View Post
    How do I find the lcd from say x-4 and x+2 (those are the denominators). Is there any rule that always works?? CanĘ't figure out this by myself.. Thanks
    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
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  3. #3
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    I would say just multiple both of the denominators to get the lcd.
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  4. #4
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    In general, you have to determine if the denominators have any common factors. For instance, the lowest common denominator in the example
    \frac{2}{(x + 3)(x - 8)}, \frac{5}{(x + 2)(x + 3)} is (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.
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