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Do Now Take out all sub work and have it on your desk for me to come around and check. Proving Angles Congruent. Objectives: 1. Identify angle pairs. 2. Prove theorems about angles. Vertical angles : angles whose sides form 2 pairs of opposite rays. ∠1 and ∠3 are vertical angles.
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Do Now Take out all sub work and have it on your desk for me to come around and check.
Proving Angles Congruent • Objectives: 1. Identify angle pairs. 2. Prove theorems about angles.
Vertical angles: angles whose sides form 2 pairs of opposite rays ∠1 and ∠3 are vertical angles
Investigation • Take out a piece of paper a draw the following figure: • Fold the sides of < 1 and < 2. • Fold the sides of < 3 and < 4. • Make a conjecture (a guess or a theory) about vertical angles.
What did you discover? • Vertical angles are congruent!
Why is this important? • We can use vertical angle congruence to find missing angle measures.
Other Types of Angle Pairs • Adjacent Angles: Two coplaner angles with a common side, a common vertex, and no common interior points.
Complementary Angles: Two angles whose measures have a sum of 90 degrees. • Each angle is called the compliment of the other.
Supplementary Angles: Two angles whose measures have a sum of 180 degrees. • Each angle is called the supplement of the other.
Linear pair: Adjacent angles whose noncommon sides are opposite rays (on a line) The measures of angles in a linear pair add to 180˚ ∠1 and ∠2 are a linear pair • m∠1 + m ∠2 = 180 ˚
Using everything wehave justlearned… how can we prove vertical angles are congruent? • We are given the information that < 1 and < 2 are vertical angles. • We want to prove that < 1 ≅< 2.
Think, Pair, Share • I am going to present you with two questions. • You will have 2 minutes to think to yourself about the question. • You will then have 3 minutes to turn to a partner and discuss the question and your response to it. • Be prepared to share your answer with the class.
Question 1 • If two angles are supplements of the same angle (or of congruent angles), are they congruent?
Question 2 • If two angles are complements of the same angle (or of congruent angles), are they congruent?