Question Video: Identifying the Legs on an Isosceles Triangle Mathematics • 11th Grade

Consider the following triangle. Identify the legs of the triangle.

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Video Transcript

Consider the following triangle. Identify the legs of the triangle. Option (A), line segment 𝐴𝐵 and line segment 𝐵𝐶. Option (B), line segment 𝐴𝐵 and line segment 𝐴𝐶. Or option (C), line segment 𝐵𝐶 and line segment 𝐴𝐶.

Let’s begin by looking at the triangle that has been drawn. Triangle 𝐴𝐵𝐶 has a side 𝐴𝐶 of three centimeters and two shorter sides each of two centimeters. This means that this must be an isosceles triangle, because by definition an isosceles triangle has two congruent sides. Line segments 𝐴𝐵 and 𝐵𝐶 are the same length of two centimeters, so we can mark on the diagram that these are congruent.

This also means that we can identify the legs of this isosceles triangle. The two congruent sides of an isosceles triangle are called the legs of the triangle. That means that we can give the answer that the two legs of this isosceles triangle are line segments 𝐴𝐵 and 𝐵𝐶, which was the answer given in option (A).

Although we weren’t asked for it here, the third side of an isosceles triangle is referred to as the base. Note that this does not have to be the side which is horizontal at the bottom of the triangle in the way we may typically have seen isosceles triangles drawn. It is simply the noncongruent third side.

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