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5
Leggy Triangles lesson 2
The Lesson GET STUDENTS READY
Answer Key
22
Warm-up on CD-ROM
individual
Here are triangles with circles.
a.
The circles are in a different place
each time.
b.
Now here are the same triangles. a.
Put the circles in the correct
places. Match the pictures above.
b.
© ETA/Cuisenaire®
Math Vocabulary Whole class
Draw a word web graphic organizer for each word:
degrees, scale. Remind students that we use a word web
to compare a word’s everyday meaning to its math
meaning. The everyday meanings and examples go
on the lines below the circle and the math meanings
and examples go on the lines above the circle. Guide
students to suggest everyday meanings and examples
for degrees [diplomas from college; second-degree
burn; temperature]; and scale. [bathroom scale; scales
on a fish] Write or draw the suggestions on the lower
lines. Then draw an angle on an upper line of the
“degrees” web. Measure and label the degrees; label
the vertex. Draw a protractor on an upper “scale” web
line. Label the numbered scale; label the vertex dot on
the base. Compare the two vertices.
DEGREES
A unit for expressing the size of an angle.
ANSWER a.
b.
COMMENTS & EXTENSIONS Rotate each of these letters
90 degrees clockwise. Then rotate each of them 90 degrees
counter-clockwise.
A O M T P
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MEASUREMENT: ANGLES, PERIMETER & AREA TOPIC 5 t LESSON 2
DAILY TANTALIZER
Just the Same
Look at each pair of shapes.
Are the shapes congruent?
1
9
5
SCALE
The measuring marks on a ruler or protractor or other
measuring tool.
K Yes
No
H Yes
B No
Foundation Skill G No
G Yes
C No
E Yes
J
I Yes
A No
E No
No
12
B Yes
J Yes
F Yes
11
8
4
H No
10
L Yes
C No
D Yes
D No
7
3
F Yes
INDIVIDUAL
I Yes
6
2
VERTEX
A point where two sides of a polygon meet; the
common endpoint of two rays that form an angle.
L
A No
K No
Congruent shapes may
not always be facing
the same direction.
Objective: Identify congruent shapes.
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6
The
lesson
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  Introduction One extension of a student’s study of angles is the classification of triangles by their angles.
When students classify, they learn to organize their thinking and they strengthen their ability
to communicate mathematical ideas.
1 Build Background WHOLE CLASS
Distribute sets of AngLegs to groups of students. Have students follow along as
you review the types of angles on the overhead with AngLegs.
Say Connect any two AngLegs together to form a right angle. Snap the
protractor onto the vertex to check the angle measure. A right angle has a
measure of 90°. You can always check for a right angle using a corner of a sheet
of paper.
Lesson Time
35 Min.
Objective
Model and identify
triangles by angles.
Materials
AngLegs™
Grouping
Whole class, then pairs
or small groups
Say Close the right angle to show a smaller angle. An angle smaller than a right
angle or 90° is an acute angle. Use your protractor to model an angle of 50°.
Say Open the angle to show an angle greater than a right angle. Your protractor
has two scales that both show the number of degrees from 0 to 180. An obtuse
angle has a measure between 90 and 180 degrees. Model an obtuse angle of 120°.
2 Model the Activity WHOLE CLASS
Ask Model a triangle using two colors of AngLegs. Do you have all acute angles
in this triangle or do you have an obtuse or right angle? If you have all acute
angles, then your triangle is an acute triangle. What would you call a triangle
that contained a right angle? [right triangle] Can you model a triangle using two
orange and one yellow AngLeg? Explain. [No, the combined lengths of the two
orange legs is the same length as the yellow leg.]
Ask Use purple, orange, and yellow legs to model a triangle. All the sides are
different lengths. You have an obtuse angle in your triangle. What word can you
use to describe it? [obtuse triangle] Can you make a triangle with one red, one
orange, and one purple AngLeg piece? [No, the red is longer than the orange
and purple put together.]
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7
Leggy Triangles lesson 2
LEGGY TRIANGLES
23
Answer Key
Name
For problems 1–3, use AngLegs to model each triangle.
Trace the inside of it below.
Label the type of triangle it is and the color of each side.
For problems 4–6, describe each triangle by its angles.
1
Right triangle
2
Acute triangle
3
Obtuse triangle
3 Guided Practice Check student work.
pairs or small groups
Prepare ahead Each small group will need
a set of AngLegs™.
If students use the shorter AngLeg pieces,
there should be enough room to trace all
their triangles on the page. Otherwise,
have them use another sheet of paper to
complete this activity. Have students share
their descriptions of their triangles for
problems 4–6.
one right angle and two acute angles
A right triangle __________________________________________________
5
all angles are acute
An acute triangle _________________________________________________
6
one obtuse angle and two acute angles
An obtuse triangle _______________________________________________
GUIDED PRACTICE
© ETA/Cuisenaire®
4
MEASUREMENT: ANGLES, PERIMETER & AREA TOPIC 5 t LESSON 2
4 Check for Understanding WHOLE CLASS
Observe students as they model the three different triangles. Provide help
as needed. Ask students to build each type of triangle.
5 Summarize WHOLE CLASS
Say Today we modeled and identified triangles by angles.
Ask What does an acute triangle look like? [Each angle is less than a right angle.]
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8
Leggy Triangles lesson 2
after
The Lesson REINFORCE THE CONCEPT
What’s My Angle?
Answer the question.
1 Two intersecting lines can make 4 right angles. True or false?
Independent Practice 2 Two intersecting lines can make 4 acute angles. True or false?
3 A triangle has 2 right angles. Always, sometimes, or never?
INDIVIDUAL
4 A triangle has 1 right angle. Always, sometimes, or never?
5 A quadrilateral has 4 angles. Always, sometimes, or never?
6 How many right angles does a rectangle have?
7 At most, how many acute angles can a parallelogram have?
8 At most, how many obtuse angles can a triangle have?
9 How many right angles does this
10 How many obtuse angles do these
11 How many obtuse angles does this
12 How many acute angles does this
figure have?
lines make?
22
figure have?
figure have?
LEGGY TRIANGLES
Answer Key
Name
Name each triangle. Write right triangle, acute triangle,
or obtuse triangle.
1
8
Always
4
False
2
2
6
obtuse triangle
Never
50
0
1
3
True
3
Sometimes
acute triangle
4
obtuse triangle
acute triangle
Objective: Describe a given geometric figure in terms of its angles.
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5
6
acute triangle
7
8
Extra Practice acute triangle
right triangle
© ETA/Cuisenaire®
on CD-ROM
individual
obtuse triangle
EXTRA PRACTICE
MEASUREMENT: ANGLES, PERIMETER & AREA 501*$ t -&440/
Theme Park Angles For 2 to 6 players
Use MeasureWorks® Game Cards, Theme Park Game Board,
People Counters, and Number (1–6) Spinner. Play is the same
as for Theme Park Angles in Lesson 1.
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