Download Triangle Notes - Perry Local Schools

Name _________________________________________________________ Period _______ Triangle Notes
I. Definitions

A triangle is a polygon that has 3 sides made of _________________________.
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The sides are joined in 3 points called ___________________________ (the plural of vertex).
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Sides that have the same number of tick marks (slashes) are __________________________.
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The sum of all the angles in a triangle is __________________. This means that if you put all of the
angles of a triangle together, they would form a _______________________ angle or a ____________.
II. Classifying Triangles Two Ways
A. By Angles
1. Acute Triangle – A triangle with ______ acute angles
2. Right Triangle – A triangle with ________ right angle and ______ acute angles
3. Obtuse Triangle – A triangle with _______ obtuse angle and _______ acute angles
4. Why can a triangle only have 1 right angle? ______________________________________________
_________________________________________________________________________________
5. Why can a triangle have only 1 obtuse angle? ____________________________________________
_________________________________________________________________________________
6. Could the same triangle contain both a right angle and an obtuse angle? _________ Explain. ______
_________________________________________________________________________________
B. By Sides
1. Equilateral Triangle – A triangle with 3 _____________ sides. All three angles are also _________.
(Hint: you almost see the word equal at the beginning of equilateral)
2. Isosceles Triangle – A triangle with 2 _____________ sides. The angles that are opposite those
sides are congruent.
(Hint: I have two eyes – isosceles begins with I and has two congruent sides)
3. Scalene Triangle – A triangle with _________ congruent sides. None of the angles are __________.
(Hint: The scum scalene triangle has nothing congruent!)
III. Practice. Classify these three triangles two different ways. First tell if it is acute, right or obtuse.
Then tell if it is equilateral, isosceles or scalene.
A ____________________________
B _________________________
C _______________________
____________________________
_________________________
________________________
IV. The Sum Of All Three Angles In A Triangle is _______________. Use this information to complete
the following questions.
A. Can these angles form a triangle? Explain.
1. 90°, 40°, 50°
2. 120°, 50°, 30°
3. 17°, 101°, 62°
4. 65°, 70°, 60°
B. Given the measurements of two angles in a triangle, find the missing angle measurement.
5. 29°, 86°, ________
6. 114°, 20°, ________
7. 60°, 40°, _________
8. 40°, 50°, _________