Question

Which statement about triangles must be true? A. A right triangle is always a scalene triangle. B. A right triangle is always an isosceles triangle. C. An isosceles triangle is always an acute triangle. D. An equilateral triangle is always an acute triangle.

Answer 1

D.

In an equilateral triangle all three angles are equal and sum to 180°, so each angle is 60°, which is acute. The other choices are false (e.g. a 45°–45°–90° triangle is right and isosceles, not scalene; a 3–4–5 triangle is right but not isosceles; an isosceles triangle can be acute, right, or obtuse).