Download Obtuse Triangle

5.1 Classifying Triangles
Warm Up
1. If the perimeter is 47, find x and the lengths of the
three sides.
2x+6 + x+3 + 3x+8 = 47
x = 5; Sides = 8; 16; 23
5.1 - Obj: Classify triangles by their angle measures
and side lengths.
Recall that a triangle ( Δ ) is a polygon with three
sides. Triangles can be classified in two ways: by
their angle measures or by their side lengths.
𝐴𝐵, BC, and AC are the sides of ΔABC.
A, B, C are the triangle's vertices.
C
A
B
Acute Triangle
Three acute angles (angles less than 90ᵒ)
Equiangular Triangle
Three congruent acute angles
Each angle is 180ᵒ 3 = 60ᵒ
Right Triangle
One right angle (90ᵒ)
Obtuse Triangle
One obtuse angle
More than 90ᵒ
Isosceles Triangle
At least two congruent sides
Equilateral Triangle
Three congruent sides
Equilateral triangles are by definition
also isosceles.
Scalene Triangle
No congruent sides
When you look at a figure, you cannot assume
segments are congruent based on appearance. They
must be marked as congruent.
Can not assume  s
Know angles are 
Can not assume 90
Know angle is 90
Classifying Triangles
Angles
Measure of
one angle is
90°
Right
Sides
Measure of
one angle is
greater than 90°
Obtuse
Measure of
all angles are
At least 2 sides
are congruent
No sides
are congruent
less than 90°
Acute
3 congruent
Angles
Equiangular
Isosceles
3 congruent
Sides
Equilateral
Scalene