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# Types of Triangles

A triangle is a polygon with three sides and three interior angles. Triangles can be classified using their side lengths and angle measures.
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## Classification by Angles

• Acute triangle: All angles are acute, or measure less than $90^\circ.$
• Obtuse triangle: Exactly one angle is obtuse, or measures between $90^\circ$ and $180^\circ,$ exclusive.
• Right triangle: One angle is a right angle, or measures $90^\circ.$
• Equiangular triangle: All angles are congruent and measure $60^\circ.$
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