Classifying Triangles

This short PowerPoint lesson introduces different classifications of triangles and illustrates their differences.

1. Classifying Triangles By That Math Lady www.thatmathlady.com © 2012

2. A triangle is a two-dimensional (flat) 3-sided shape. What is a triangle? These are some examples of triangles. www.thatmathlady.com © 2012

3. You can classify triangles by the measurement of their interior angles. If a triangle has one 90° angle, it is called a right triangle . If a triangle has one obtuse angle, it is called an obtuse triangle . If a triangle has three acute angles, it is called an acute triangle . Let’s look at some examples of these triangles… Classifying by Angles www.thatmathlady.com © 2012

4. A right triangle must have one angle that measures 90° exactly. RIGHT TRIANGLES How do you know if an angle is 90°? Place the corner of a piece of paper in the angle. If the border of the triangle aligns with the sides of the paper, you know it is a right angle! 90° www.thatmathlady.com © 2012

5. An obtuse triangle must have one angle that is greater than 90°. OBTUSE TRIANGLES www.thatmathlady.com © 2012

6. An acute triangle has 3 acute angles. Each angle must measure less than 90°. ACUTE TRIANGLES What kind of sign is this? What kind of triangle? www.thatmathlady.com © 2012

7. You can classify triangles by the side lengths and angle measurements. If a triangle has 3 equal side lengths, it is called an equilateral triangle . If a triangle has 2 equal side lengths, it is called an isosceles triangle . If a triangle has no equal side lengths, it is called a scalene triangle . Let’s look at some examples of these triangles… Classifying by Side Lengths www.thatmathlady.com © 2012

8. Equilateral triangles are made up of three equal side lengths and three 60° angles. It has three lines of symmetry. EQUILATERAL TRIANGLES 3 ft 3 ft 3 ft 60° 60° 60° www.thatmathlady.com © 2012

9. Isosceles triangles are made up of two equal side lengths and two equal angles. It has one line of symmetry. ISOSCELES TRIANGLES www.thatmathlady.com © 2012

10. Scalene triangles are made up of 3 side lengths and 3 angles that are all different sizes and measurements. It does not have any lines of symmetry. SCALENE TRIANGLES www.thatmathlady.com © 2012

11. It has a right angle… All the sides are different lengths... What kind of triangle is this? www.thatmathlady.com © 2012

12. Yes! This is a right scalene triangle! What kind of triangle is this? www.thatmathlady.com © 2012

13. It has an obtuse angle… Two sides have identical lengths... What kind of triangle is this? www.thatmathlady.com © 2012

14. Yes! This is an obtuse isosceles triangle! What kind of triangle is this? www.thatmathlady.com © 2012

15. It has three acute angles… All the sides have different lengths... What kind of triangle is this? www.thatmathlady.com © 2012

16. Yes! This is an acute scalene triangle! What kind of triangle is this? www.thatmathlady.com © 2012

17. Now You Know… how to classify triangles based on their angles. how to classify triangles based on their side lengths. words such as isosceles , scalene , and equilateral . In Summary www.thatmathlady.com © 2012