In the last lesson, you learned that triangles can be classified, or named, based on the length of their sides.
Now, we're going to learn another way to classify triangles, based on their angles.
A triangle is a shape that has three straight sides and three angles.
What is a side?
A side is a line segment that joins the vertices of a shape to one another.
What is an angle?
An angle is the opening that two sides make.
Important:
The sum of the angles of any triangle always equal 180°.
Let's now look at the three types of triangles.
An acute triangle is a triangle with 3 acute angles.
Tip: An acute angle is less than 90°.
This means that the angles in an acute triangle are all less than 90°.
Tip: If we add up the three angles of any triangle, they always equal 180°.
40° + 70° + 70° = 180°
Tip: Every triangle has at least one acute angle, but only acute triangles have exactly three.
A right triangle is a triangle with exactly 1 right angle.
A right angle is exactly 90°.
The other two angles in a right triangle will both always be acute.
An obtuse triangle is a triangle with 1 obtuse angle.
An obtuse angle is greater than 90°.
Let's look at the types of triangles, classified by angle, again.
Now, complete the practice. It will help you remember for longer.