Question

How many lines of symmetry are in this isosceles triangle?

• A. 1
• B. 3
• C. 2
• D. 4

Answer 1

Answer: (A)

An isosceles triangle has one line of symmetry. However, if the isosceles triangle is also an equilateral triangle, then it has three lines of symmetry.

But the given triangle is not an equilateral triangle.

An isosceles triangle is defined as a triangle with two sides of equal length. An equilateral triangle is defined as a triangle with three sides of equal length. Therefore, an equilateral triangle is also an isosceles triangle.

This triangle has 2 sides of equal length. When an isosceles triangle has exactly two sides of equal length, then it has just 1 line of symmetry that runs from the vertex between the two sides of equal length to the midpoint of the side opposite that vertex.

So option A is the correct answer.