Lesson: Constructing and Analyzing Triangles
Different types of triangles
To measure the angles of a triangle:
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Center a protractor on the vertex of the angle.
Use the ray that extends upward as a pointer to the correct angle measures.
To construct triangles:
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Use a ruler to measure and draw in the given side length(s).
Use a protractor to measure and construct given angles.
Join angles and side lengths together to form 3 vertices.
Key Concepts
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The angles in a triangle always sum to 180 degrees.
In a triangle, the largest angle is opposite the largest side, and the smallest angle is opposite the
smallest side.
The sum of two side lengths of a triangle should always be greater or equal to the length of the
third side.
Not all combination of segments or angles will form triangles.
Practice Questions
1. Which three side lengths could make a triangle?
A.
9 cm, 25 cm, 12 cm
B.
12 cm, 21 cm, 34 cm
C.
14 cm, 6 cm, 18 cm
D.
30 cm, 31 cm, 63 cm
2. What is the measure of angle x?
a.
20°
b.
70°
c.
80°
d.
110°
3. Zoe’s math teacher tells her to construct an equilateral triangle. What information does Zoe
need?
a.
the measures of the angles
b.
the measure of one of the sides
c.
the ratio between the different side lengths
d.
the ratio between the different angle measures