Answer
Factor out $-1$ from one of the denominators
Work Step by Step
Consider the sum of two rational expressions:
$$E=\dfrac{5}{x-3}+\dfrac{2}{3-x}.$$
To add the two rational expressions with opposite denominators we factor out $-1$ from one of the denominators:
$$E=\dfrac{5}{x-3}+\dfrac{2}{-(x-3)}=\dfrac{5}{x-3}+\dfrac{-2}{x-3}.$$
Now we have the same denominator to both rational expressions, so we can perform the addition:
$$E=\dfrac{5+(-2)}{x-3}=\dfrac{3}{x-3}.$$
The last step is to simplify the result if possible. In our case it is not possible.
