1. 4-1, 4-2: Classify Triangle & Angle Relationships
4/23/2017
4-1 and 4-2
Classifying Triangles
Angle Relationships in Triangles
M217 - Denna

2. Classify Triangles By Angles
Type
Definition
Drawing/Example
Acute
Right
Obtuse
Equiangular

3. Classify Triangles By Sides
Type
Definition
Drawing/Example
Scalene
Isosceles
Equilateral

4. Classify each triangle by angles and sidesK
115◦
25◦
40◦
70◦ E A N S
∆ NSE
∆ ANE
∆ AEK
∆ ASK
∆ AES 6 8 11 10 12
5.1

5. Find the value of x, y and ∆ side lengths6) 7)
2 – 4x
13 – 2x
x2 – 5x – 15 6y
4y + 12
10x – 4

6. 8) You are bending a wire to make a coat hanger
8) You are bending a wire to make a coat hanger. The length of the wire is 65 cm. You need 25 cm to make the hook of the hanger. The triangular portion of the hanger is an isosceles triangle. The length of one leg of this triangle is half the length of the base.
a) Sketch the hanger.
b) Give the dimensions of the triangular portion.

7. Triangle Sum Theorem
The sum of the angles measures of a triangle is ____________________. Corollaries of the Thm
Acute angles in a right triangle are complementary.
Measure of each angle in an equiangular triangle is 60◦.

8. Exterior Angle Theorem
The measure of an exterior angle of a triangle is equal to the sum of the measures of its remote (nonadjacent) interior angles. 4 3 2 1
𝑚<4=𝑚<1+𝑚<2

9. Third Angles Theorem
If two angles of one triangle are congruent to two angles of another triangle, then the third angles are ____________.
70◦
50◦
50◦
70◦

10. Ex: Apply the new theorems to solve
10)
In ∆SMD, m<S=55 and m<M is four times larger than m<D. Find m<M and m<D. 9)