In an equilateral triangle, which property holds?

• A. All three sides are equal in length.
• B. The triangle has a right angle.
• C. The triangle is scalene.
• D. The base is perpendicular to the height.

Answer: (A)

In an equilateral triangle, all three sides are equal in length. That defining feature explains why the triangle is perfectly symmetric: with every side the same, each interior angle is also equal, and in fact they measure 60 degrees each.

The other statements don’t describe what’s unique about equilateral triangles. A right angle would contradict the equal-angle pattern of 60-degree angles. A scalene triangle has all sides of different lengths, which isn’t the case here. The idea that the base is perpendicular to the height is true for any triangle because the height is defined as a line from a vertex that is perpendicular to the opposite side, so this property isn’t unique to equilateral triangles.