Transcript Glencoe Geometry - Dolfanescobar's Weblog

Five-Minute Check (over Lesson 2–7)
NGSSS
Then/Now
Postulate 2.10: Protractor Postulate
Postulate 2.11: Angle Addition Postulate
Example 1: Use the Angle Addition Postulate
Theorems 2.3 and 2.4
Example 2: Real-World Example: Use Supplement or Complement
Theorem 2.5: Properties of Angle Congruence
Proof: Symmetric Property of Congruence
Theorems 2.6 and 2.7
Proof: One Case of the Congruent Supplements Theorem
Example 3: Proofs Using Congruent Comp. or Suppl. Theorems
Theorem 2.8: Vertical Angles Theorem
Example 4: Use Vertical Angles
Theorems 2.9–2.13: Right Angle Theorems
Over Lesson 2–7
Justify the statement with a property of equality or
a property of congruence.
A. Transitive Property
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D. Segment Addition Postulate
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B
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C. Reflexive Property
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B. Symmetric Property
Over Lesson 2–7
Justify the statement with a property of equality or
a property of congruence.
A. Transitive Property
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B
D. Segment Addition Postulate
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B
C
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C. Reflexive Property
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B. Symmetric Property
Over Lesson 2–7
Justify the statement with a property of equality or
a property of congruence.
If H is between G and I, then GH + HI = GI.
A. Transitive Property
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B
D. Segment Addition Postulate
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C. Reflexive Property
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B. Symmetric Property
Over Lesson 2–7
State a conclusion that can be drawn from the
statements given using the property indicated.
W is between X and Z; Segment Addition Postulate.
A. WX > WZ
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D. WZ – XZ = XW
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B
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C. XW + XZ = WZ
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B. XW + WZ = XZ
Over Lesson 2–7
State a conclusion that can be drawn from the
statements
given using the property indicated.
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LM  NO
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D.
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Over Lesson 2–7
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Given B is the midpoint of AC, which of the
following is true?
A. AB + BC = AC
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B
D. BC = 2AB
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B
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D
C. AB = 2AC
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B. AB + AC = BC
MA.912.G.8.5 Write geometric proofs,
including proofs by contradiction and proofs
involving coordinate geometry. Use and
compare a variety of ways to present
deductive proofs, such as flow charts,
paragraphs, two-column, and indirect proofs.
You identified and used special pairs of angles.
(Lesson 2–7)
• Write proofs involving supplementary and
complementary angles.
• Write proofs involving congruent and right
angles.
Use the Angle Addition Postulate
CONSTRUCTION Using a protractor, a construction
worker measures that the angle a beam makes with
a ceiling is 42°. What is the measure of the angle
the beam makes with the wall?
The ceiling and the wall make a 90 angle. Let 1 be
the angle between the beam and the ceiling. Let 2 be
the angle between the beam and the wall.
m1 + m2 = 90
42 + m2 = 90
42 – 42 + m2 = 90 – 42
m2 = 48
Angle Addition Postulate
m1 = 42
Subtraction Property of
Equality
Substitution
Use the Angle Addition Postulate
Answer: The beam makes a 48° angle with the wall.
Find m1 if m2 = 58 and mJKL = 162.
A. 32
B. 94
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D. 116
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C. 104
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Use Supplement or Complement
TIME At 4 o’clock, the angle between the hour and
minute hands of a clock is 120º. When the second
hand bisects the angle between the hour and minute
hands, what are the measures of the angles between
the minute and second hands and between the
second and hour hands?
Understand Make a sketch of the
situation. The time is 4
o’clock and the second
hand bisects the angle
between the hour and
minute hands.
Use Supplement or Complement
Plan
Use the Angle Addition Postulate and the
definition of angle bisector.
Solve
Since the angles are congruent by the
definition of angle bisector, each angle
is 60°.
Answer: Both angles are 60°.
Check
Use the Angle Addition Postulate to check
your answer.
m1 + m2 = 120
60 + 60 = 120 
QUILTING The diagram below shows
one square for a particular quilt
pattern. If mBAC = mDAE = 20,
and BAE is a right angle, find
mCAD.
A.
B.
C.
D.
C. 40
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D. 50
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B. 30
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A. 20
Proofs Using Congruent Comp. or Suppl.
Theorems
Given:
Prove:
Proofs Using Congruent Comp. or Suppl.
Theorems
Proof:
Statements
Reasons
1. m3 + m1 = 180
1 and 4 form a
linear pair.
2. 1 and 4 are
supplementary.
2. Linear pairs are
supplementary.
3. 3 and 1 are
supplementary.
3. Definition of
supplementary angles
4. 3  4
4. s suppl. to same 
are .
1. Given
In the figure, NYR and RYA form a linear pair,
AXY and AXZ form a linear pair, and RYA and
AXZ are congruent. Prove that NYR and AXY
are congruent.
Which choice correctly completes the proof?
Proof:
Statements
Reasons
1.
1. Given
linear pairs.
2.
2. If two s form a
linear pair, then
they are suppl. s.
3.
3. Given
4. NYR  AXY
?
4. ____________
A. Substitution
B. Definition of linear pair
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D. Definition of
supplementary s
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C. s supp. to the same  or
to  s are .
Use Vertical Angles
If 1 and 2 are vertical angles and m1 = d – 32
and m2 = 175 – 2d, find m1 and m2.
1  2
m1 = m2
d – 32 = 175 – 2d
Vertical Angles Theorem
Definition of congruent
angles
Substitution
3d – 32 = 175
Add 2d to each side.
3d = 207
Add 32 to each side.
d = 69
Divide each side by 3.
Use Vertical Angles
m1 = d – 32
= 69 – 32 or 37
m2 = 175 – 2d
= 175 – 2(69) or 37
Answer: m1 = 37 and m2 = 37
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