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# Download 3-3 Parallel and Perpendicular Lines

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Transcript

Parallel and Perpendicular Lines LESSON 3-3 Additional Examples Suppose that the top and bottom pieces of a picture frame are cut to make 60° angles with the exterior sides of the frame. At what angle should the two sides be cut to ensure that opposite sides of the frame will be parallel? In order for the opposite sides of the frame to be parallel, same-side interior angles must be supplementary. Two 90° angles are supplementary, so find an adjacent angle that, together with 60°, will form a 90° angle: 90° – 60° = 30°. Quick Check HELP GEOMETRY Parallel and Perpendicular Lines LESSON 3-3 Additional Examples Study what is given, what you are to prove, and the diagram. Then write a paragraph proof. Given: In a plane, a s, c s, and a b. Prove: c b Proof: Lines a and c are both perpendicular to line s, so a c because two lines perpendicular to the same line are parallel. It is given that a b. Therefore , c b because two lines parallel to the same line are parallel to each other. Quick Check HELP GEOMETRY