Algebra: A Combined Approach (4th Edition)

Yes $\frac{5-x}{x-5}$ can be simplified
Step 1: The terms in the numerator and denominator become similar if -1 is taken common from the two terms in the numerator. $\frac{5-x}{x-5}$ = $\frac{-(x-5)}{x-5}$ Step 2: The similar terms can be cancelled to give $-1$