7.2: Triangles
- Page ID
- 194231
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Triangle Basics
- All triangles have three sides. (File this fact under the “thank you Captain Obvious” category.)
- All triangles contain 180 degrees.
Figure 9. Triangle
Isosceles triangle. This triangle has two sides that are equal, and two angles that are equal.
Figure 10. Isosceles triangle
Equilateral triangle. All three sides of this triangle are equal, and all three of its angles are equal too.
Figure 11. Equilateral triangle
Similar triangles. These triangles each have different sized sides, but they share the same sized angles.
Figure 12. Similar triangles
Right triangles. These triangles have one right angle (equal to 90 degrees). This means that the other two angles are complementary, that is, they must add to 90 degrees.
Figure 13. Complementary angles.
Scalene triangle. These triangles have three sides all of different lengths.
Obtuse triangle. These triangles have one obtuse angle, so one angle whose measure is greater than 90 degrees.
Acute triangle. These triangles have three acute angels, so all three angles measure less than 90 degrees.
It is possible to describe a triangles based on two key characteristics, its side lengths (equilateral, isosceles or scalene) and its angle measures (right, obtuse or acute).
Classify each triangle by angle and side. For example, “acute scalene”.)
1. 
2. 
3. 
- Answer
-
1. right isosceles triangle
2. obtuse scalene triangle
3. acute equilateral triangle (yes, an equilateral triangle will always be acute)