TRI006 · Triangles · Classes 6–9
Obtuse triangle
An obtuse triangle has one angle greater than 90°. With c the longest side, a² + b² < c².
> 90°Obtuse triangle
📐 Formula
obtuse ⇔ a² + b² < c² (c longest)
✏️ Worked example
Sides 3, 4, 6: 9 + 16 = 25 < 36, so it is obtuse; the largest angle ≈ 117.3°.
🌍 Where it is used
Recognising shapes in bridges and ramps.
❓ Quick check
How many obtuse angles can a triangle have?
🏋️ Practice
EasyIs 2, 3, 4 obtuse?
Answer: Yes (4 + 9 < 16)
MediumAngles 100°, 50°, 30°: type?
Answer: Obtuse
ChallengeIs 7, 8, 9 obtuse?
Answer: No (acute)