FTCE General Knowledge Math Practice Test

A triangle in which two sides are of equal length is known as what type of triangle?

1. Equilateral triangle

2. Isosceles triangle

3. Acute triangle

4. Scalene triangle

The correct answer is: Isosceles triangle

A triangle in which two sides are of equal length is known as an isosceles triangle. By definition, an isosceles triangle has at least two sides that are of equal length, which also means that the angles opposite these sides are equal. This property is significant in various mathematical contexts, such as when calculating perimeters or areas, as well as in geometric proofs. The equilateral triangle is a specific type of isosceles triangle where all three sides are equal, leading to all angles being equal to 60 degrees. An acute triangle refers to a triangle where all three angles are less than 90 degrees, but it does not necessarily have any equal sides. A scalene triangle, on the other hand, is characterized by having all sides of different lengths, meaning it does not have any equal sides. Thus, the distinguishing characteristic of an isosceles triangle lies in its pair of equal sides.