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Learn about same-side interior angles in parallel lines with examples and proofs. Identify corresponding and supplementary angles.
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Same-side interior angles are on the same side of transversal t between lines p and q. 4, 8, and 5 are on the same side of the transversal as 1, but only 1 and 8 are interior. So 1 and 8 are same-side interior angles. Properties of Parallel Lines LESSON 3-1 Additional Examples Use the diagram above. Identify which angle forms a pair of same-side interior angles with 1. Identify which angle forms a pair of corresponding angles with 1.
The angle corresponding to 1 must lie in the same position relative to line q as 1 lies relative to line p. Because 1 is an interior angle, 1 and 5 are corresponding angles. Properties of Parallel Lines LESSON 3-1 Additional Examples (continued) Corresponding angles also lie on the same side of the transversal. One angle must be an interior angle, and the other must be an exterior angle. Quick Check
Compare 2 and the vertical angle of 1. Classify the angles as alternate interior angles, same-side interior angles, or corresponding angles. The vertical angle of 1 is between the parallel runway segments. 2 is between the runway segments and on the opposite side of the transversal runway. Because alternate interior angles are not adjacent and lie between the lines on opposite sides of the transversal, 2 and the vertical angle of 1 are alternate interior angles. Properties of Parallel Lines LESSON 3-1 Additional Examples Quick Check
1. Given 1. a b 2. Corresponding Angles Postulate 2. m 1 = m3 3. m 3 + m 4 = 180 3. Angle Addition Postulate 4. Substitution 4. m 1 + m 4 = 180 5. Definition of supplementary angles 5. 1 and 4 are supplementary Properties of Parallel Lines LESSON 3-1 Additional Examples Use the given that a b and the diagram to write a two-column proof that 1 and 4 are supplementary. Quick Check
In the diagram above, || m. Find m 1 and then m 2. 1 and the 42° angle are corresponding angles. Because || m, m 1 = 42 by the Corresponding Angles Postulate. Because 1 and 2 are adjacent angles that form a straight angle, m 1 + m 2 = 180 by the Angle Addition Postulate. If you substitute 42 for m 1, the equation becomes 42 + m 2 = 180. Subtract 42 from each side to find m 2 = 138. Properties of Parallel Lines LESSON 3-1 Additional Examples Quick Check
Properties of Parallel Lines LESSON 3-1 Additional Examples In the diagram above, || m. Find the values of a, b, and c. a = 65 Alternate Interior Angles Theorem c = 40 Alternate Interior Angles Theorem a + b + c = 180 Angle Addition Postulate 65 + b + 40 = 180 Substitution Property of Equality b = 75 Subtraction Property of Equality Quick Check