Types of angles
Identify acute and obtuse angles; compare and order angles up to two right angles by size
What a learner can do afterwards
- Classify given angles as acute, right, or obtuse
- Order four angles from smallest to largest by visual comparison
- Identify all acute and obtuse angles in a given triangle or quadrilateral
The lesson
You already know a right angle: the square corner of a book or a piece of paper. Not every angle is a right angle. Some angles are smaller than a right angle. We call those acute angles. Some angles are bigger than a right angle. We call those obtuse angles.
At 5 o'clock, the hands spread further apart. That angle is bigger than a right angle, so it's obtuse. The wider the gap between the hands, the bigger the angle.
When you compare angles, look at how wide they open, not how long the lines are drawn. A short angle can still be obtuse, and a long angle can still be acute.
Smaller than a right angle is acute, bigger than a right angle is obtuse, and you compare the opening, not the length of the lines.
Watch it
Where it sits
Learn first
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.