7-2 Parallel and Perpendicular Lines Warm Up Problem of the Day Lesson Presentation Course 3

7-2 Parallel and Perpendicular Lines Warm Up Complete each sentence. Course 3 7-2 Parallel and Perpendicular Lines Warm Up Complete each sentence. 1. Angles whose measures have a sum of 90° are _______________ . 2. Vertical angles have equal measures, so they are ______________. 3. Angles whose measures have a sum of 180° are ______________. 4. A part of a line between two points is called a ____________. complementary congruent supplementary segment

7-2 Parallel and Perpendicular Lines Problem of the Day Course 3 7-2 Parallel and Perpendicular Lines Problem of the Day The square root of 1,813,141,561 is a whole number. Is it odd or even? How do you know? Odd: An odd number can only be the product of two odd numbers.

Course 3 7-2 Parallel and Perpendicular Lines Learn to identify parallel and perpendicular lines and the angles formed by a transversal.

Insert Lesson Title Here Course 3 7-2 Parallel and Perpendicular Lines Insert Lesson Title Here Vocabulary parallel lines perpendicular lines transversal

7-2 Parallel and Perpendicular Lines Course 3 7-2 Parallel and Perpendicular Lines Parallel lines are lines in a plane that never meet, like a set of perfectly straight, infinite train tracks. Perpendicular lines are lines that intersect at 90° angles.

7-2 Parallel and Perpendicular Lines Course 3 7-2 Parallel and Perpendicular Lines The railroad ties are transversals to the tracks. The tracks are parallel. A transversal is a line that intersects two or more lines that lie in the same plane. Transversals to parallel lines form angles with special properties.

7-2 Parallel and Perpendicular Lines Caution! Course 3 7-2 Parallel and Perpendicular Lines You cannot tell for certain if angles are congruent by measuring because measurement is not exact. Caution!

7-2 Parallel and Perpendicular Lines Course 3 7-2 Parallel and Perpendicular Lines Additional Example 1: Identifying Congruent Angles Formed by a Transversal Measure the angles formed by the transversal and parallel lines. Which angles seem to be congruent? 1, 3, 5, and 7 all measure 150°.  2, 4, 6, and 8 all measure 30°.

Additional Example 1 Continued Course 3 7-2 Parallel and Perpendicular Lines Additional Example 1 Continued Angles marked in blue appear to be congruent to each other, and angles marked in red appear to be congruent to each other. 1 @ 3 @ 5 @ 7 2 1 3 4 2 @ 4 @ 6 @ 8 6 5 7 8

7-2 Parallel and Perpendicular Lines Check It Out: Example 1 Course 3 7-2 Parallel and Perpendicular Lines Check It Out: Example 1 Measure the angles formed by the transversal and parallel lines. Which angles seem to be congruent? 1 2 3 4 5 6 7 8 1, 4, 5, and 8 all measure 36°.  2, 3, 6, and 7 all measure 144°.

Check It Out: Example 1 Continued Course 3 7-2 Parallel and Perpendicular Lines Check It Out: Example 1 Continued Angles marked in blue appear to be congruent to each other, and angles marked in red appear to be congruent to each other. 1 @ 4 @ 5 @ 8 2 @ 3 @ 6 @ 7 1 2 3 4 5 6 7 8

7-2 Parallel and Perpendicular Lines Course 3 7-2 Parallel and Perpendicular Lines If two lines are intersected by a transversal and any of the angle pairs shown below are congruent, then the lines are parallel. This fact is used in the construction of parallel lines.

PROPERTIES OF TRANSVERSALS TO PARALLEL LINES Course 3 7-2 Parallel and Perpendicular Lines PROPERTIES OF TRANSVERSALS TO PARALLEL LINES If two parallel lines are intersected by a transversal, the acute angles that are formed are all congruent, the obtuse angles are all congruent, and any acute angle is supplementary to any obtuse angle. If the transversal is perpendicular to the parallel lines, all of the angles formed are congruent 90° angles.

7-2 Parallel and Perpendicular Lines Writing Math Course 3 7-2 Parallel and Perpendicular Lines The symbol for parallel is ||. The symbol for perpendicular is . Writing Math

7-2 Parallel and Perpendicular Lines m4 = 124° Course 3 7-2 Parallel and Perpendicular Lines Additional Example 2A: Finding Angle Measures of Parallel Lines Cut by Transversals In the figure, line l || line m. Find the measure of the angle. 4 All obtuse angles in the figure are congruent. m4 = 124°

7-2 Parallel and Perpendicular Lines Course 3 7-2 Parallel and Perpendicular Lines Additional Example 2B: Finding Angle Measures of Parallel Lines Cut by Transversals Continued In the figure, line l || line m. Find the measure of the angle. 2 2 is supplementary to the angle 124°. m2 + 124° = 180° –124° –124° m2 = 56°

7-2 Parallel and Perpendicular Lines m6 = 56° Course 3 7-2 Parallel and Perpendicular Lines Additional Example 2C: Finding Angle Measures of Parallel Lines Cut by Transversals Continued In the figure, line l || line m. Find the measure of the angle. 6 All acute angles in the figure are congruent. m6 = 56°

7-2 Parallel and Perpendicular Lines m7 = 144° Course 3 7-2 Parallel and Perpendicular Lines Check It Out: Example 2A In the figure, line n || line m. Find the measure of the angle. 7 All obtuse angles in the figure are congruent m7 = 144° 1 144° 3 4 5 6 7 8 m n

7-2 Parallel and Perpendicular Lines Check It Out: Example 2B Course 3 7-2 Parallel and Perpendicular Lines Check It Out: Example 2B In the figure, line n || line m. Find the measure of the angle. 5 5 is supplementary to the angle 144°. 1 144° 3 4 5 6 7 8 m n m5 + 144° = 180° –144° –144° m 5 = 36°

7-2 Parallel and Perpendicular Lines m1 = 36° Course 3 7-2 Parallel and Perpendicular Lines Check It Out: Example 2C In the figure, line n || line m. Find the measure of the angle. 1 All acute angles in the figure are congruent m1 = 36° 1 144° 3 4 5 6 7 8 m n

7-2 Parallel and Perpendicular Lines Lesson Quiz In the figure a || b. Course 3 7-2 Parallel and Perpendicular Lines Lesson Quiz In the figure a || b. 1. Name the angles congruent to 3. 1, 5, 7 2. Name all the angles supplementary to 6. 1, 3, 5, 7 3. If m1 = 105° what is m3? 105° 4. If m5 = 120° what is m2? 60°