Chapter P, Prerequisites - Section P.7 - Rational Expressions - P.7 Exercises - Page 51: 28

$\frac{1-x}{1+x}$

We factor the left side and reduce: $\displaystyle \frac{x^{2}+2x-3}{x^{2}-2x-3}*\displaystyle \frac{3-x}{3+x}=\frac{(x+3)(x-1)}{(x-3)(x+1)}*\frac{-(x-3)}{x+3}=\frac{-(x-1)}{x+1}=\frac{-x+1}{x+1}=\frac{1-x}{1+x}$