Which triangle has all interior angles less than 90 degrees?

• A. Right Triangle
• B. Acute Triangle
• C. Obtuse Triangle
• D. Equilateral Triangle

Answer: (B)

All interior angles less than 90 degrees defines an acute triangle. In such a triangle every angle is sharp, staying under a right angle. A right triangle has one angle exactly 90 degrees, so it doesn’t fit the condition. An obtuse triangle has one angle greater than 90, which also fails. An equilateral triangle has all angles equal to 60 degrees, which does satisfy the condition, but the standard term that describes the whole figure by this property is acute triangle, making it the best answer to this description.