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3-7 Perpendicular Lines Lines that intersect at an angle of 90 degrees are perpendicular lines. For example, let’s say that we have the line AB and the line CD Now, if the lines intersect at an angle of C 90o, A D then AB CD. B Perpendicular lines are lines that intersect to form a right angle. m Definition of Perpendicular Lines Symbols: m n n m 1 2 4 3 n If two lines are perpendicular, then they form 4 right angles. a Theorem 3-8 1 2 4 3 Symbols: a b b In the figure, OP MN and NP QS. Determine whether each of the following is true or false. 1 False. Since OP MN, 2 P M 1 5 2 R 6 Q True. are vertical angles, and vertical angles are congruent. 3 7 O True. If two lines are perpendicular, then they form 4 right angles. 4 QR PR False. 8 3 S 4 N