Canadian Forces Aptitude Test (CFAT) Practice

What is the defining characteristic of an isosceles triangle?

1. It has three equal sides

2. It has two equal angles

3. It has a right angle

4. It has acute angles

The correct answer is: It has two equal angles

An isosceles triangle is defined by having at least two sides that are of equal length. This characteristic inherently leads to the conclusion that the angles opposite those equal sides are also equal, making two angles congruent. This property is fundamental to the definition of an isosceles triangle and sets it apart from other types of triangles. While it is true that an equilateral triangle has three equal sides and angles, an isosceles triangle only needs a minimum of two equal sides and their corresponding angles. The options that refer to specific angle types, like having a right angle or all acute angles, do not apply universally to isosceles triangles since an isosceles triangle can have varying angle types, including right or obtuse angles. Therefore, the defining characteristic of an isosceles triangle is indeed the presence of two equal angles, arising directly from the equal lengths of its sides.