Lessons on Triangles

eLearning for 1/21

TRIANGLES INTRO

Basic Triangle Facts

• A triangle is a polygon with 3 straight sides coming to 3 points.

• The sum of the interior (inside) angles of a triangle is 180 degrees.

• Triangles can be classified by their angles and sides.

Classification of Triangles by their
SIDES & ANGLES

Multiple Choice

Classify this triangle by its sides:

• Scalene

• Equilateral

• Isosceles

Multiple Choice

Classify this triangle by its angles

• Acute

• Obtuse

• Right

Multiple Choice

What is triangle ABC classified by side length?

• Scalene

• Right

• Equilateral

• Acute

Multiple Choice

What is triangle ABC classified as using angles?

• Obtuse

• Right

• Acute

• Equilateral

Multiple Choice

What is triangle DEF classified as using angles?

• Acute

• Obtuse

• Right

• Scalene

How to Find the Missing Angle in a Triangle

• Since all the the interior angles of a triangle add up to 180 degrees, we can find a missing angle if we know the measurement of 2 other angles.

• Simply add together the two angles you know, and subtract that value from 180 to find the missing angle.

Multiple Choice

What is the value of the missing angle?

Click the picture if you need to!

• 90°

• 52°

• 128°

Multiple Choice

What is the measure of ∠B?

• 30

• 67

• 45

Multiple Choice

What is the measure of ∠F?

Hint: What does the box in the corner mean?

• 180

• 90

• 45

Multiple Choice

What is the measure of ∠I?

• 71

• 50

• 59

Multiple Choice

What is the measure of each of the angles in triangle ABC?

Hint: What kind of triangle is it?

• 90

• 30

• 45

• 60

Multiple Choice

What is the measure of ∠F?

• 34

• 28

• 62