Classifying Triangles

www.thatmathlady.com © 2012

Classifying TrianglesBy That Math Lady


A triangle is a two-dimensional (flat) 3-sided shape.

What is a triangle?

These are some

examples of triangles.


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


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°


An obtuse triangle must have one angle that is greater than 90°.

OBTUSE TRIANGLES


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?


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


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 ft60°

60°60°


Isosceles triangles are made up of two equal side lengths and two equal angles. It has one line of symmetry.

ISOSCELES TRIANGLES


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


It has a right angle… All the sides are different lengths...

What kind of triangle is this?


Yes! This is a right scalene triangle!



It has an obtuse angle… Two sides have identical lengths...



Yes! This is an obtuse isosceles triangle!



It has three acute angles… All the sides have different lengths...



Yes! This is an acute scalene triangle!



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

Classifying Triangles

Education

Transcript of Classifying Triangles