Determine if a triangle is acute, obtuse, or right based on its sides or angles.
Triangle Sides
Classification
Acute Triangle
Triangle Type
Largest Angle78.5°
Is Acute?Yes
Area14.70
About this calculator
Acute vs Obtuse vs Right
A triangle is classified by its largest internal angle. If all angles are less than 90°, it is an acute triangle. If one angle is exactly 90°, it is a right triangle. If one angle is greater than 90°, it is an obtuse triangle.
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Pro Tips
For a triangle to be acute, the square of the longest side must be LESS than the sum of the squares of the other two sides.
In a right triangle, c² = a² + b² (Pythagorean Theorem).
In an obtuse triangle, c² > a² + b².
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Fun Facts
"Every equilateral triangle is an acute triangle (all angles are 60°)."
"The word 'acute' comes from the Latin 'acutus', meaning sharp."
"In spherical geometry, the sum of angles can exceed 180°, and a triangle can have three right angles!"
Formula: c² < a² + b² (for Acute, where c is the longest side)
