5.2.3 Slopes of Parallel and Perpendicular Lines (continued) Example 2 Geometry Application In Example 2, Prof. Burger finds the slope of each side of a quadrilateral, and then uses those slopes to show that the quadrilateral is a parallelogram. Note that in a parallelogram, the opposite sides of the figure are parallel.
Example 3 Identifying Perpendicular Lines
To determine whether two nonvertical lines are perpendicular, multiply their slopes. If the product of the two slopes is − 1, then the two lines are perpendicular. Note that vertical lines are perpendicular to horizontal line, and not perpendicular to any other line.
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