Geometry
Name:____________________________
4.1 & 4.2 Notes: Classifying Triangles
and Angle Measures of Triangles
A triangle can be classified by its sides and its angles.
Equilateral Triangle
Isosceles Triangle
Example 1:
Classify the triangles by its sides.
1.
5
Scalene Triangle
2.
5
3.
6
10
5
8
17
6
15
Equiangular Triangle
Acute Triangle
Right Triangle
Obtuse Triangle
Example 2:
Classify the triangles by its angles.
4.
5.
6.
45⁰
20⁰
70⁰
115⁰
50⁰
60⁰
Example 3:
Classify the triangle by its angles and by its sides.
7.
8.
60⁰
3
3
60⁰
60⁰
9.
27
12
75⁰
12
7
15⁰
50⁰
50⁰
TRY:
A ____________________________________ of a triangle is a point that joins two sides of the
triangle. The side across from an angle is the __________________ side.
Example 1: Name the side that is opposite the angle.
a) ∠A
b) ∠B
c) ∠C
Theorem 4.1: Triangle Sum Theorem
Example 2: Find m∠C.
A _______________________ to a theorem is ______________________________________________.
Corollary to the Triangle Sum Theorem:
Example 3: Find the measure of ∠1.
Example 4: ∆𝐴𝐵𝐶 𝑎𝑛𝑑 ∆𝐴𝐵𝐷 are right triangles. Suppose m∠ABD = 35˚.
a) Find m∠DAB.
b) Find m∠BCD.
Try: 1. Find m∠1.
2. Find m∠C.
The angles inside the triangle are the
_____________________ angles. When the sides of a
triangle are extended, the angles adjacent to the interior angles are the ___________________
angles.
Exterior angles always form a ____________________ with an interior angle.
Theorem 4.2: Exterior Angle Theorem
The measure of an exterior angle of a triangle is equal to
______________________________________________________.
Example 5: Find m∠1.
HW: p. 177 #25 – 35 odds, #47 – 53 odds and p. 182 #3 – 14, 18 – 21, 23, 26