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
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
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.