## Algebra and Trigonometry 10th Edition

The slope is critical when determining if lines are parallel, perpendicular, or neither. Since the equations are given in point slope form (y = mx + b), the slope will be the value of m. In this example, the lines and slopes are: $y_{1}$ = $\frac{-4}{5}$x - 5 where m = $\frac{-4}{5}$ $y_{2}$ = $\frac{5}{4}$x + 1 where m = $\frac{5}{4}$ If the slopes of the two lines are the same, then the lines are parallel. If the slopes of the two lines are negative reciprocals, then the lines are perpendicular. Using this rule, the two lines are perpendicular since $\frac{-4}{5}$ is the negative reciprocal of $\frac{5}{4}$.