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2.2. What’s the Relationship? Pg. 6 Complementary, Supplementary, and Vertical Angles. 2.2 – What's the Relationship?________________ Complementary, Supplementary, and Vertical Angles
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2.2 What’s the Relationship? Pg. 6 Complementary, Supplementary, and Vertical Angles
2.2 – What's the Relationship?________________ Complementary, Supplementary, and Vertical Angles In Chapter 1, you compared shapes by looking at similarities between their parts. For example, two shapes might have sides of the same length or equal angles. In this chapter you will examine relationships between parts within a single shape or diagram. Today you will start by looking at angles to identify relationships in a diagram that make angle measures equal.
2.10 – ANGLE RELATIONSHIPS When you know two angles have a certain relationship, learning something about one of them tells you something about the other. Certain angle relationships come up often enough in geometry that we given them special names.
14 90 – 76 = 76
118 180 – 62 = 62
23 157 157 23
23 CEB 157 157 23
54 126 126 54
b. Based on your observations, write a conjecture (a statement based on an educated guess that is unproven). Start with , "Vertical angles are ...“ Vertical angles are _________________. congruent
2.12 – PROVING VERTICAL ANGLES CONGRUENT The last problem used what is called inductive reasoning to show that vertical angles are congruent. We are now going to start to use deductive reasoning to prove that all vertical angles are congruent, no matter what the angles measure. Below you are given the steps in order to prove that vertical angles are congruent. Your job is to explain why each statement is true. Match the reasons with the given statements.
A. Both add to 180 B. Straight angles add to 180 C. Subtract y from both sides D. Straight angles add to 180 Straight angles add to 180 Straight angles add to 180 Both add to 180 Subtract y from both sides
40 90 50 40
2.14 –ANGLES RELATIONSHIPS In the problems below, you will use geometric relationships to find angle measures. Start by finding a special relationship between some of the angles, and use that relationship to write an equation. Solve the equation for the variable, then use that variable to find the missing measurement.
28 supplementary Angle Relationship: __________________ Equation: __________________________ PNM = ____________________________ x = 28 x + 152 = 180 28
23 congruent Angle Relationship: __________________ Equation: __________________________ FGH = ____________________________ x = 7 4x – 5 = 3x + 2 23
36 complementary Angle Relationship: __________________ Equation: __________________________ DBC = ____________________________ x = 29 3x + 3 = 90 36
76 supplementary Angle Relationship: __________________ Equation: __________________________ QPM = ____________________________ x = 76 2x + 28 = 180 76
2.15 – SUMMARY Discuss each different type of angle measurement: right, complementary, straight, supplementary, congruent, and vertical. What is their relationship? Are they equal or add to something? Draw a picture of each.
Angles that add to 90 One 90 angle
Angles that add to 180 One 180 angle
P S 1 2 Q R Opposite angles that are congruent Angles with same degree