Concept 2 of 9
Types of Angles
Today's big idea
Compare with 90° and 180°: acute, right, obtuse, straight, reflex, in that order.
Vertically opposite angles are EQUAL. Linear pair = 180°.
How it works
👀 What's going on?
A door can swing open a little, or a lot, or all the way back to the wall. Every one of those swings is an angle. The only question is how much turn it holds.
💡 Here's the trick
Look at the diagram above. An angle is the turn between two arms that meet at a corner, counted in degrees. Under 90° it is acute, and at exactly 90° it is right. Between 90° and 180° it is obtuse, at exactly 180° it is straight, and beyond that it is reflex. Angles on a straight line add to 180°, and angles round a point add to 360°.
🪄 How to do it
- 1.Hold the angle in the diagram above against a square corner.
- 2.Name it acute, right, obtuse, straight or reflex.
- 3.For a missing angle, subtract from 180° or from 360°.
- 4.Where two lines cross, copy a size across to the angle facing it.
✍️ Try it
A clock reads 3 o'clock. What type of angle do the two hands make? Then: the hands move on to 5 o'clock. What type is the angle between them now?
At 3 o'clock the hands are a quarter turn apart, which is 90°, so it is right. At 5 o'clock they are five hour-steps apart, and each step is 30°, giving 150°, which is obtuse.
⚠️ Watch out
You might be thinking that a bigger drawing means a bigger angle. Stretch both arms to twice the length and the turn between them does not change. Angle size depends on the turn alone, never on how long the arms are.
🌟 Why this matters
A skateboard ramp, a reclining chair and the tilt of a solar panel are all set by angle. Roof builders choose a slope so that rain runs off instead of sitting still. Once you can name a turn you can copy it, check it and describe it.
Exam tip: Sketch a corner beside any angle you are unsure of, then compare the two.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“An angle measures 205°. What TYPE is it?”
- 1
Compare with 180°
205 > 180 — bigger than a straight line. 📐
- 2
Compare with 360°
205 < 360 — less than a full turn.
- 3
Match the type
Between 180° and 360° → reflex.
- 4
Answer ✓
205° is reflex.
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
CHALLENGE 1 OF 4
Drag the ray to make a 60° angle
Quick check
✅ VERIFICATION
A turn of 200° is which type of angle?
⚡ Finish the activity above first to answer.
Keep going!
Up next: Triangles by Sides
3 equal · 2 equal · 0 equal.