# Acute Triangle Definition

In geometry, an **acute triangle**, also known as an acute-angled triangle, is defined as the **triangle having all side’s angles less than a right angle or 90°**.

In contrast, a triangle with all side’s angles more than 90° is an obtuse triangle. In an acute-angled triangle, each of the three internal angles of the triangle is acute and measured less than 90°.

The difference between a right-angle triangle and acute-angled triangles is that; in a right-angle triangle, at least one side of it forms an angle equivalent to 90°, as shown in the diagram below;

**Note:**

To know about alternate exterior angle, you can use our Alternate Exterior Definition.

Whereas, in an acute angle, all the three angles are measured less than 90°, as shown in the diagram below;