Triangles are polygons with three sides and three angles. The size of the angles determines what kind of triangle it is.
All the angles inside a triangle always add up to 180 degrees.
An acute triangle is a triangle where all three angles are less than 90 degrees.
If every angle is less than 90°, the triangle is always acute.
A right triangle has one angle that measures exactly 90 degrees. A 90-degree angle is shown with a small square in the corner.
Right triangles are often used in real life, such as in construction, ramps, and tools like squares.
An obtuse triangle is a triangle that has one angle greater than 90 degrees.
A triangle can only have one obtuse angle, because the angles must add up to 180°.
Each triangle type is named for the largest angle inside it.
When classifying triangles, always check the angles first. The biggest angle decides the type of triangle.