3.2 Angles Formed by Parallel Lines and Transversals
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Transcript 3.2 Angles Formed by Parallel Lines and Transversals
Welcome!
1. Take out your homework and a red pen
2. Take out a protractor
3. Start working on the back of your notes from
yesterday
Row #?
3.2: Angles Formed by Parallel
Lines and Transversals
Learning Objective :
SWBAT prove and use theorems about the angles
formed by parallel lines and a transversal.
Whiteboards: Review
Identify each of the following.
1. a pair of parallel segments
EH || FG
2. a pair of skew segments
BF and EH
3. a pair of perpendicular segments
CG GH
4. a pair of parallel planes
plane ABC and plane EFG
Whiteboards
Identify each angle pair.
1. 1 and 3
2. 3 and 6
3. 4 and 5
4. 6 and 7
3.2 Angles Formed by Parallel Lines
and Transversals
What would you call two lines that are on the same plane bdo not
intersect?
Exterior
B
A
Interior
D
C
Exterior
• A solid arrow placed on
two lines of a diagram
indicate the lines are
parallel.
• The symbol || is used to
indicate parallel lines.
• AB || CD
3.2 Angles Formed by Parallel Lines
and Transversals
A slash through the parallel symbol || indicates the
lines are not parallel.
AB || CD
B
A
D
C
3.2 Angles Formed by Parallel Lines
and Transversals
Special Angle Relationships WHEN THE LINES
ARE PARALLEL
♥Alternate Interior Angles
Exterior
are CONGRUENT
1
3 4
Interior
5 6
7 8
Exterior
2
♥Alternate Exterior Angles are
CONGRUENT
♥Same Side Interior Angles are
SUPPLEMENTARY
♥Same Side Exterior Angles are
SUPPLEMENTARY
3.2 Angles Formed by Parallel Lines
and Transversals
Example 1
Find mQRS.
3.2 Angles Formed by Parallel Lines
and Transversals
Example 2
Find each angle measure.
a. mECF
b. mDCE
3.2 Angles Formed by Parallel Lines
and Transversals
Example 3
Find the measure of each angle.
a. mEDG
b. mBDG
Example 4
Find mABD.
2x + 10° = 3x – 15°
x = 25
mABD = 2(25) + 10 = 60°
Alt. Int. s Thm.
Subtract 2x and add 15 to both sides.
Substitute 25 for x.
Example 5:
Find x and y in the diagram.
By the Alternate Interior Angles
Theorem, (5x + 4y)° = 55°.
By the Corresponding Angles Postulate, (5x +
5y)° = 60°.
5x + 5y = 60
–(5x + 4y = 55)
y=5
5x + 5(5) = 60
x = 7, y = 5
Subtract the first equation from the second
equation.
Substitute 5 for y in 5x + 5y = 60. Simplify and
solve for x.
Whiteboards
State the theorem or postulate that is related to the measures of
the angles in each pair. Then find the unknown angle measures.
1. m1 = 120°, m2 = (60x)°
Alt. Ext. s Thm.; m2 = 120°
2. m2 = (75x – 30)°,
m3 = (30x + 60)°
Corr. s Post.; m2 = 120°, m3 = 120°
3. m3 = (50x + 20)°, m4= (100x – 80)°
Alt. Int. s Thm.; m3 = 120°, m4 =120°
4. m3 = (45x + 30)°, m5 = (25x + 10)°
Same-Side Int. s Thm.; m3 = 120°, m5 =60°
Lesson Overview
Standards: A.CED.3
MP: 1,2,3,4,5
Vocabulary: Transversal, ….
Essential Question:
Learning Objective: Prove and use theorems about the angles
formed by parallel lines and a transversal.
Independent Practice: Pg. 148 #6-13, 26-29, 34, 42