8.2 Angles and Triangles

p. 411

Acute Angle

O An angle whose measure is less than 90º

Obtuse Angle

O An angle whose measure is greater than 90º

Right Angle

O An angle whose measure is exactly 90º

Classify Triangles

By Angle Measure By Side Lengths

O Acute

O Obtuse

O Right

O Equilateral

O Isosceles

O Scalene

Acute Triangle

O An acute triangle has three acute angles (all

angles less than 90°)

Right Triangle

O A right triangle has one right angle

Obtuse Triangle

O An obtuse triangle has one obtuse angle

(one angle greater than 90°)

Equilateral Triangle

O An equilateral triangle has three congruent

sides.

Isosceles Triangle

O An isosceles triangle has two congruent

sides.

Scalene Triangle

O A scalene triangle has NO congruent sides.

Naming Geometric Figures

O A geometric figure can be named

using the vertices of each of its

angles. Use either a clockwise or

counterclockwise order such as

O Tick marks in a drawing show that

side lengths are equal. Arc marks

show than angle measures are equal.

Example 1

O Classify triangle XYZ by its angles

O Classify triangle XYZ by its side lengths

Triangles

O The sum of all three angles in a triangle is

always 180°

A

C B

∠𝐴 + ∠𝐵 + ∠𝐶 = 180°

Example 2A

O Find the value of x, then classify the triangle

by its angle measures.

Example 2B

O Find the value of x, then classify the triangle

by its angle measures.

Independent Practice p. 413 1-22, 28-32, 39-44