Classify Triangles by their Angles worksheet - Free Printable

Let’s go through each triangle one by one and decide if it’s acute (A), right (R), or obtuse (O).

Remember:
- Acute triangle → all angles are less than 90°
- Right triangle → one angle is exactly 90° (looks like a perfect corner)
- Obtuse triangle → one angle is more than 90° (looks “wide” or “stretched”)

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Triangle 1: All angles look smaller than 90°. It’s tall and pointy — definitely acute.
→ A

Triangle 2: Also looks like all angles are small. Even though it’s shorter, no wide or square corners.
→ A

Triangle 3: One angle is very wide — clearly bigger than 90°. That makes it obtuse.
→ O

Triangle 4: Has a perfect L-shape corner — that’s a right angle!
→ R

Triangle 5: Tiny but still all angles look sharp and under 90°.
→ A

Triangle 6: Looks like a right triangle too — vertical and horizontal sides meet at a square corner.
→ R

Triangle 7: Upside down, but still all angles are small. No wide or square corners.
→ A

Triangle 8: Very stretched out — one angle is super wide, definitely over 90°.
→ O

Triangle 9: All angles look less than 90° — even the big ones aren’t wide enough to be obtuse.
→ A

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Final Answer:
1. A
2. A
3. O
4. R
5. A
6. R
7. A
8. O
9. A