Skill: Classify triangles by side lengths

To classify a triangle by its side lengths, compare the lengths of all three sides.

• Scalene: all three sides have different lengths.
• Isosceles: exactly two sides have the same length.
• Equilateral: all three sides have the same length.

Example

A triangle has side lengths $7\text{ cm}$, $5\text{ cm}$, and $7\text{ cm}$. Classify the triangle.

1. List the side lengths:

$$7\text{ cm},\ 5\text{ cm},\ 7\text{ cm}$$

2. Compare the lengths. Two sides are equal:

$$7\text{ cm}=7\text{ cm}$$

3. The third side is different, so all three sides are not equal.

4. Therefore, the triangle is isosceles.

The triangle’s position, size in a drawing, or angle measures do not affect its classification. Use only the side lengths.