Isosceles Triangle and Equilateral Triangle

Draw

DO NOW TUESDAY.

Encircle the letter of your answer

Classifying Triangles

Classifying triangles by their sides and lengths

• Triangles have special names based on their side lengths and angle measures.

  
  

  
  

• When you classify triangles by their side lengths, you use the words equilateral, isosceles, and scalene.

Equilateral Triangle

• An equilateral triangle has three equal sides.

• This is an example of a equilateral triangle.

Multiple Choice

Which of these triangles is equilateral?

Isosceles triangle

• An isosceles triangle has two equal sides.

• This is an example of an isosceles triangle.

Multiple Choice

Which of these triangles is isosceles?

Scalene Triangle

• A scalene triangle has no equal sides.

• This is an example of scalene triangle.

Multiple Choice

Which of these triangles is scalene?

Classifying triangles by angle measure

• When you classify triangles by their angle measures, you use the words acute, right, and obtuse.

  
  

• Let's find out what those words mean!

Acute Triangle

• An acute triangle has 

  three acute angles.

• Acute angles measure less than 90°

• This is an example of an acute triangle.

Multiple Choice

Which of these is an acute triangle?

Right Triangle

• A right triangle has one right angle.

• Right angles measure exactly 90°.

• This is an example of a right triangle.

• Notice that all of the angles add up to 180 degrees.

• The angles in a triangle always add up to 180 degrees

Multiple Choice

Which of these is a right triangle?

Obtuse triangle

• An obtuse triangle has one obtuse angle.

• Obtuse angles measure more than 90°.

• This is an example of an obtuse triangle.

Multiple Choice

Which of these triangles is obtuse?

Classifying triangles two ways

• This is a right isosceles triangle.

• It has a right angle and two equal sides.

Classifying Triangles

Topic 12 Lesson 2

​How to Remember?

• ​Equilateral: "equal"-lateral (lateral means side) so they have all equal sides

• Isosceles: means "equal legs", and we have two legs, right?   Also iSOSceles has two equal "Sides" joined by an "Odd" side.

• Scalene: means "uneven" or "odd", so no equal sides.

Triangles can be classified by the measure of their angles.

​

HOW DO ANGLES CLASSIFY TRIANGLES?

​

Theorem:

The sum of the interior angles of a triangle is 180 degrees.

It follows that the acute angles of a right triangle are complementary.

Multiple Choice

Classify the triangle.

• Acute Triangle

• Right Triangle

• Obtuse Triangle

Multiple Choice

Classify the triangle.

• Acute Triangle

• Right Triangle

• Obtuse Triangle

Multiple Choice

Which measurements are true for a isosceles triangle (in cm)

• 5,6 and 7

• 9,9 and 3

• 0, 10 and 20

Multiple Choice

Classify the triangle by its sides: 2cm, 2cm, 2cm

• equilateral

• isosceles

• scalene

Multiple Choice

Classify the triangle by its sides: 9m, 8m, 10m

• equilateral

• isosceles

• scalene

Multiple Choice

What is the characteristics of an equilateral triangle?

• Two sides are equal

• All three sides and all three angles are equal

• No sides are equal

Multiple Choice

Which pair of angles is congruent?

• <A and <B

• <A and <C

• <B and <C

Multiple Choice

What is the value of x?

• 12

• 11

• 8

• 6

Multiple Choice

What is the value of z?

• 86

• 68

• 44

• 34

Multiple Choice

What is the value of x?

• 72

• 67

• 65

• 54

Multiple Choice

What is the value of x?

• 41

• 45

• 31

• 98

Multiple Choice

What is the measure of the Top Left Angle.

• 55

• 27.5

• 125

• 110

Multiple Choice

The sides of an equilateral triangle have...

• different measures.
• Mr M's gallon of water

• equal measures.
• 60°.

Multiple Choice

What is the measure of ∠S?

• not enough information

• 30

• 60

• 180

Multiple Choice

Find x

• 10
• 32
• 116
• 16

Multiple Choice

What is the measurement of angle J and K?

• m∠J= 68, m∠K= 136

• m∠J= 68, m∠K= 44

• m∠J= 67, m∠K= 77

• m∠J= 44, m∠K= 68