Answer
When you use the LCD to add or subtract rational expressions, the answer will not always be in the simplest form. This is because once added or subtracted together, the new numerator may have common factors with the denominator that would now need to be divided out of the problem.
Work Step by Step
Example:
$\frac{9}{2y+4} - \frac{5}{2y+4} =\frac{9-5}{2y+4} = \frac{4}{2y+4}$
Now we can reduce the fraction by factoring out 2 from the denominator and dividing:
$ \frac{4}{2y+4} = \frac{4}{2(y+2)} = \frac{2}{y+2} $
