In geometry, acute is defined as any angle measuring more than zero but less than 90 degrees. An acute triangle is one in which all three interior angles are acute.
An obtuse angle measures more than 90 degrees but less than 180 degrees. An obtuse triangle contains one angle that is obtuse. By the definition of a triangle, the other two angles are both acute.
In a right triangle, there is one interior angle that measures exactly 90 degrees. Each of the other two angles is acute and the sum of the acute angles is equivalent to 90 degrees. Examples of standard right triangles include the 30-60-90 degree right triangle and the 45-45-90 degree right triangle.
An equilateral triangle is a specific type of acute triangle. An equilateral triangle has three equal sides and three equal angles. Each interior angle of an equilateral triangle is 60 degrees.
A triangle that has two equal sides and two equal angles is known as an isosceles triangle. An isosceles triangle can be an acute, obtuse or right, depending on the measurement of the third angle. A standard 45-45-90 right triangle is an example of an isosceles triangle.
A triangle with no equal sides or angles is known as a scalene triangle. Scalene triangles can be acute, obtuse or right triangles.