Ontario Mathematics Proficiency Practice Test

An isosceles triangle is defined by having at least two equal sides. This characteristic is what sets it apart from other types of triangles. In an isosceles triangle, because of the two equal sides, the angles opposite these sides are also equal. This property is crucial in various applications in geometry, such as in calculating angles or solving problems involving triangle properties.

The other definitions relate to different types of triangles. A triangle with no equal sides describes a scalene triangle, where all sides and angles are different. A triangle where all three sides are equal is known as an equilateral triangle, a specific case of isosceles but with an additional restriction. Finally, a triangle that includes one right angle is referred to as a right triangle, which is based solely on its angle measures rather than the lengths of its sides. Thus, the defining feature of two equal sides distinctly classifies an isosceles triangle.