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3.7 Perpendicular Lines in the Coordinate Plane. Postulate 18 “Slopes of Perpendicular Lines”. In a coordinate plane, 2 non-vertical lines are perpendicular if and only if the product of their slopes is -1. Vertical and Horizontal Lines are Perpendicular.
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Postulate 18“Slopes of Perpendicular Lines” In a coordinate plane, 2 non-vertical lines are perpendicular if and only if the product of their slopes is -1. Vertical and Horizontal Lines are Perpendicular.
Example 1: Deciding whether the lines are perpendicular. Line h: The slope of h is 3/4. Line j: The slope of j is -4/3. So the lines are perpendicular.
Example 2: Deciding whether the lines are perpendicular. Line a: The slope of a is -2/3. Line b: The slope of b is -3/2. So the lines are NOT perpendicular. The Product needs to be -1.
Example 3: Deciding whether the lines are perpendicular. Line r: Line s: The product of the slopes is 1, not -1. So, r and s are not perpendicular.
Example 4: Find an equation of a perpendicular line. Line t has an equation . Find an equation of the line s that passes through P(4,0) and is perpendicular to t.