When you add rational expressions, you may need to factor a trinomial to find
the LCD. Study
the sample below. Then simplify the expressions in Exercises 46–49.
$$\text { Sample: } \frac{2 x}{x^{2}-1}+\frac{3}{x^{2}+x-2}=\frac{2
x}{(x+1)(x-1)}+\frac{3}{(x-1)(x+2)}$$
The LCD is \((x+1)(x-1)(x+2)\)
Note: If you just used \(\left(x^{2}-1\right)\left(x^{2}+x-2\right)\) as the
common denominator, the factor \((x-1)\) would be included twice.
$$\frac{5 x-1}{2 x^{2}-7 x-15}-\frac{-3 x+4}{2 x^{2}+5 x+3}$$