Exercise: Identifying Angles in Triangles and Quadrilaterals
How do we name an angle?
When we write ∠ABC, it means:
• The middle letter (B) is the vertex of the angle
• The first letter (A) is on one side of the angle
• The last letter (C) is on the other side of the angle
In each question you will see a shape with several angles - click on the correct angle!
Part A - Triangle
Click on the angle:
∠BAC
The vertex is A (the middle letter)
Pay attention: the middle letter is A!
Look for the angle at vertex A (at the top)
Look for the angle at vertex A (at the top)
🎉 Correct! 🎉
∠BAC is the angle at vertex A.
Its sides are AB and AC.
Its sides are AB and AC.
Part B - Triangle
Click on the angle:
∠CBA
The vertex is B (the middle letter)
Pay attention: ∠CBA is the same as ∠ABC!
The vertex is B (bottom left)
The vertex is B (bottom left)
🎉 Excellent! 🎉
∠CBA (= ∠ABC) is the angle at vertex B.
You can write it in either direction - what matters is that the vertex is in the middle!
You can write it in either direction - what matters is that the vertex is in the middle!
Part C - Quadrilateral
Click on the angle:
∠DAB
The vertex is A (the middle letter)
Pay attention: the vertex is A!
This is the angle at the top left corner
This is the angle at the top left corner
🎉 Great! 🎉
∠DAB is the angle at vertex A.
Its sides are AD and AB.
Its sides are AD and AB.
Part D - Quadrilateral
Click on the angle:
∠DCB
The vertex is C (the middle letter)
Pay attention: ∠DCB is the same as ∠BCD!
The vertex is C (at the bottom right corner)
The vertex is C (at the bottom right corner)
🎉 Well done! 🎉
∠DCB (= ∠BCD) is the angle at vertex C.
Its sides are CD and CB.
Its sides are CD and CB.
Part E - Triangle with Interior Line
Click on the angle:
∠ADB
The vertex is D (the middle letter)
Pay attention: the vertex is D!
There are two angles at vertex D - this one is between AD and DB (left side)
There are two angles at vertex D - this one is between AD and DB (left side)
🎉 Excellent! 🎉
∠ADB is the angle at vertex D,
between sides DA and DB (the left angle at point D).
between sides DA and DB (the left angle at point D).
Part F - Triangle with Interior Line
Click on the angle:
∠CAD
The vertex is A (the middle letter)
Pay attention: ∠CAD is the same as ∠DAC!
The vertex is A, and this is the right-side angle at vertex A (between AC and AD)
The vertex is A, and this is the right-side angle at vertex A (between AC and AD)
🎉 Well done! 🎉
∠CAD (= ∠DAC) is the angle at vertex A,
between sides AC and AD (the right part of the top angle).
between sides AC and AD (the right part of the top angle).
🌟 Well Done! 🌟
You successfully identified all the angles!
What we learned:
• The middle letter in the angle notation is always the vertex
• The side letters are on the two sides of the angle
∠ABC = ∠CBA
(You can write it in either direction - what matters is that the vertex is in the middle!)
• When there is an interior line (like AD), additional angles are formed!