Download Classify triangles

Name ——————————————————————————
LESSON
17.3
G OAL
Date ——————————————
CA Standards
MG 2.2
MG 2.3
Reteach
For use with pages 468–474
Classify triangles.
VOCABULARY
Sum of angle measures of a triangle The sum of the measures
of the angles in any triangle is 180.
Congruent sides of a figure have the same length.
Classifying Triangles by Angle Measures
An acute triangle has three acute angles.
A right triangle has one right angle.
An obtuse triangle has one obtuse angle.
Classifying Triangles by Side Lengths
EX AM PLE
Lesson 17.3
An equilateral triangle has 3 congruent sides.
A isosceles triangle has at least 2 congruent sides.
A scalene triangle has no congruent sides.
1 Finding an Angle Measure in a Triangle
Find the value of x in the triangle shown.
Solution
Copyright © Houghton Mifflin Company.
x 57 36 180
x 93 180
x 87
Answer: The value of x is 87.
Sum of angle measures
in a triangle is 180.
Add 57 and 36.
Subtract 93 from each side.
x
57
36
Exercises
for Example 1
.................................................................................................
Find the value of y.
1.
2.
40
100
42
y
y
50
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Name ———————————————————————
LESSON
Reteach
17.3
Date ——————————
CA Standards
MG 2.2
MG 2.3
continued
For use with pages 468–474
E X A M P LE
2 Classifying a Triangle by Angle Measures
Classify the triangle by its angle measures.
25⬚
Solution
125⬚
30⬚
The triangle has one obtuse angle so it is an obtuse triangle.
Exercises
for Example 2
.................................................................................................
Classify the triangle by its angle measures.
3. 30⬚, 60⬚, 90⬚
E X A M P LE
4. 47⬚, 56⬚, 77⬚
3 Drawing Triangles
Lesson 17.3
Use a protractor and a ruler to draw an obtuse scalene triangle with one
angle measure of 130°.
Solution
Step 1
Step 2
Use a ruler to draw
AB.
a segment }
Use a protractor
to
]›so that it
draw AX
forms a 130° angle
AB.
with }
X
X
0 10
180 170 1 20
60
170 180
60
0
0 1 20 10
15
0 30
14 0
4
80 90 100
70 100 90 80 110 1
70
2
60 0 110
60 0 1
2
3
50 0 1
50 0
3
1
A
]›
Draw point C on AX
such that AC ⫽ AB.
Then connect B and C.
B
C
A
B
Exercises
for Example 2
.................................................................................................
5. Draw an acute isosceles triangle with one angle measure of 45°.
Copyright © Houghton Mifflin Company.
B
3
15 0 4
01 0
40
A
Step 3
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