An angle is made of two rays with the same starting point.
You've learned about 5 types of angles.
An acute angle is any angle that measures less than 90 degrees.
These are examples of acute angles:
A right angle is exactly 90 degrees:
The two line segments that form right angles are perpendicular to each other.
An obtuse angle is any angle that is greater than 90 degrees but less than 180 degrees.
The angles below are obtuse.
Now, let's classify, or name, shapes based on the angles that they form.
Which of these shapes have an acute angle?
Let’s check.
This parallelogram and this rhombus have acute angles:
All triangles have at least one acute angle.
An acute triangle is a special triangle with exactly three acute angles, not just one.
Which shapes have a right angle? 🤔
There are two! The square and the rectangle.
Only some triangles have a right angle.
Triangles with a right angle are called right triangles.
Tip: The rhombus and parallelogram can have right angles too, but then we usually call them squares and rectangles instead.
Which shapes have an obtuse angle?
The trapezoid, the hexagon, and the pentagon always have an obtuse angle.
Some triangles have obtuse angles.
An obtuse triangle is a triangle with one obtuse angle.
Great job learning how to classify shapes according to angles.
Now, try the practice. It's fun, and will help you remember for longer.