Which statement best defines an acute triangle?

Which statement best defines an acute triangle?

• A. A triangle with one angle of 90 degrees.
• B. A triangle that contains only angles that are less than 90 degrees.
• C. A triangle with all sides equal.
• D. A triangle with one angle greater than 180 degrees.

Answer: (B)

Triangles are classified by angle measures. An acute triangle has all three interior angles less than 90 degrees. This defining trait means every angle is acute, so the whole triangle is acute. If one angle is 90 degrees, it becomes a right triangle, not acute; if an angle were greater than 180 degrees, that would violate how triangles add up in Euclidean geometry. A triangle with all sides equal is called equilateral, which is always acute, but that describes a side property rather than the angle-based criterion for acuteness. So, all interior angles being less than 90 degrees best defines an acute triangle.

Triangles are classified by angle measures. An acute triangle has all three interior angles less than 90 degrees. This defining trait means every angle is acute, so the whole triangle is acute. If one angle is 90 degrees, it becomes a right triangle, not acute; if an angle were greater than 180 degrees, that would violate how triangles add up in Euclidean geometry. A triangle with all sides equal is called equilateral, which is always acute, but that describes a side property rather than the angle-based criterion for acuteness. So, all interior angles being less than 90 degrees best defines an acute triangle.