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OTCQ Given: ABC is a straight angle and BD ABC. Prove ABD is a right angle.

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OTCQ Given:  ABC is a straight angle and BD ABC. Prove  ABD is a right angle. D. Statements. Reasons. A. B. C. OTCQ # 100609 Given:  ABC is a straight angle and BD ABC. Prove  ABD is a right angle. D. Statements. Reasons. A. B. C. 1.Given. - PowerPoint PPT Presentation
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OTCQ Given: ABC is a straight angle and BD ABC. Prove ABD is a right angle. A B C D Statements Reasons
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Page 1: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

OTCQGiven: ABC is a straight angle and BD ABC. Prove ABD is a right angle.

A B C

DStatements Reasons

Page 2: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

OTCQ # 100609Given: ABC is a straight angle and BD ABC. Prove ABD is a right angle.

A B C

DStatements Reasons

1. ABC is a straight angle and BD ABC.

Conclusion: ABD is a right angle

1.Given.

Page 3: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

OTCQ # 100609Given: ABC is a straight angle and BD ABC. Prove ABD is a right angle.

A B C

DStatements Reasons

1. ABC is a straight angle and BD ABC. 2. If BD ABC, then the intersection of BD and ABC forms 2 right angles: ABD and DBCConclusion: ABD is a right angle

1.Given.

2. Definition of perpendicular.

QED. Quo era demonstratum

Page 4: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Aim 4-3 How do we prove theorems about angles (part 2)?

GG 30, GG 32, GG 34

Page 5: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

OBJECTIVE1. SWBAT prove angle theorems.2. SWBAT recall some basic

definitions.

Page 6: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Prove Theorem 4-2 If two angles are straight angles, then they are congruent.

A

ED

CB

F

Statements Reasons1. Given

2. Definition of straight angle.3.Definition of straight angle.

4.Definition of congruent. QED

Given ABC is a straight angle and DEF is a Straight angle. Prove ABC DEF.

1. ABC is a straight angle and DEF is a straight angle.

2. m ABC = 180○

3. m DEF = 180○.

Conclusion ABC DEF.

Page 7: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem 4-1: If 2 angles are right angles, then they are congruent.

Theorem 4-1: If 2 angles are straight angles, then they are congruent.

Adjacent angles: are two angles in the same plane that have a common vertex and a common side, but do not have any interior points in common.

Page 8: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Complementary angles are two angles the sum of whose degree measures is 90○.

Supplementary angles are two angles the sum of whose degree measures is 180○.

Page 9: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are complements of the same angle then they are congruent.

Why?

Page 10: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are complements of the same angle then they are congruent.

Why?Givenm 1= 45○

m 2= 45○

m 3= 45○

13

2

Page 11: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are complements of the same angle then they are congruent.

Why?Givenm 1= 45○

m 2= 45○

m 3= 45○

13

2

m1+ m 2= 90○ , hence 2 is the complement of 1.m1+ m 3= 90○ , hence 3 is the complement of 1.Since 2 and 3 are each the complement of 1,then 2 and 3 must be congruent.

Page 12: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are congruent then their complements are congruent.

Why?

Page 13: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are congruent then their complements are congruent.

Why?Givenm 1= 30○

m 2= 30○ 1

3

24

Page 14: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are congruent then their complements are congruent.

Why?Givenm 1= 30○

m 2= 30○

If 3 is complementary to 1, what is the degree measure of 3?

If 4 is complementary to 2, what is the degree measure of 4?

1

32

4

Page 15: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are congruent then their complements are congruent.

Why?Givenm 1= 30○

m 2= 30○

If 3 is complementary to 1, what is the degree measure of 3? (90○ - 30○ = 60○)

If 4 is complementary to 2, what is the degree measure of 4?

1

32

4

Page 16: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem 4-4: If 2 angles are congruent then their complements are congruent.

Why? 3 4Givenm 1= 30○

m 2= 30○

If 3 is complementary to 1, what is the degree measure of 3? (90○ - 30○ = 60○)

If 4 is complementary to 2, what is the degree measure of 4? (90○ - 30○ = 60○)

1

32

4

Page 17: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are supplements of the same angle then they are congruent.

Why?Please try to draw 2 angles that are

supplementary to the same angle.

Page 18: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are supplements of the same angle then they are congruent.Given: ABC is a straight angle, we can say that ABE is a supplement to EBC.

A E

D

B

C

Page 19: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are supplements of the same angle then they are congruent.Given: ABC is a straight angle, we can say that ABE is a supplement to EBC.

A E

D

B

CNext, given that DBE is a straight angle, we can say that DBC is a supplement to EBC.

Page 20: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are supplements of the same angle then they are congruent.Given: ABC is a straight angle, we can say that ABE is a supplement to EBC.

A E

D

B

CNext, given that DBE is a straight angle, we can say that DBC is a supplement to EBC.

Conclusion: ABE DBC

Page 21: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are supplements of the same angle then they are congruent.Given: ABC is a straight angle, we can say that ABE is a supplement to EBC.

A E

D

B

CNext, given that DBE is a straight angle, we can say that DBC is a supplement to EBC.

Conclusion: ABE DBC

65○

65○

115○

Page 22: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are congruent then their supplements are congruent.

Why?

Page 23: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are congruent then their supplements are congruent.Given: ABC is a straight angle.DBE is a straight angle.ABE DBC

A E

D

B

C

Conclusion: ABD EBC

65○

65○

115○

Page 24: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 angles are congruent then their supplements are congruent.Given: ABC is a straight angle.DBE is a straight angle.ABE DBC

A E

D

B

C

Conclusion: ABD EBC

65○

65○

115○115○

Page 25: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Linear pair of angles:2 adjacent angles whose sum is a straight angle.

ABE and EBC are a linear pair of angles.

The others?

A E

D

B

C

65○

65○

115○115○

Page 26: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Linear pair of angles:2 adjacent angles whose sum is a straight angle.

ABE and EBC are a linear pair of angles.The others?EBC and CBD.CBD and DBA.DBA and ABE.There should always be 4 pairs of linear pairs when 2 lines intersect.

A E

D

B

C

65○

65○

115○115○

Why 4 pairsof linear pairs?

Page 27: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Linear pair of angles:2 adjacent angles whose sum is a straight angle.

ABE and EBC are a linear pair of angles.The others?EBC and CBD.CBD and DBA.DBA and ABE.There should always be 4 pairs of linear pairs when 2 lines intersect.

A E

D

B

C

65○

65○

115○115○

Theorem: Linear pairs of angles are supplementary.

Page 28: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 lines intersect to form congruent adjacent angles, then they are perpendicular.

1

3

2

4

Page 29: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Theorem: If 2 lines intersect to form congruent adjacent angles, then they are perpendicular.

Since m1 + m 2 =180○ and 1 2, we may substitute to say

m 1 + m 1 =180○ and then2 m 1 =180○ and then

2 m 1 =180○ and then 2 2m 1 =90○

We can do the same for 2, 3 and 4

1

3

2

4

Page 30: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Vertical angles:2 angles in which the sides of one angle are opposite rays to the sides of the second angle.Theorem 4-9.If two lines intersect, then the vertical angles are congruent.

Vertical angles:EBC and ABD.ABE and DBC.There should always be 2 pairs of vertical angles pairs when 2 lines intersect.

A E

D

B

C

65○

65○

115○115○

Page 31: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

34

G

F

E

H

1 2

D

C

B

AGiven: ADC EHG 1 4

Prove: 2 3Statements Reasons

Page 32: OTCQ Given:   ABC is a straight angle and  BD     ABC. Prove  ABD is a right angle.

Recall Properties of Equality

1) Reflexive: a = a2) Symmetric: If a = b then b = a.3) Transitive:

If a = b and b = c, then a = c.4) Substitution: If a = b, then a can be replaced by b.


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