Skill: Classify triangles by side lengths

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

• Equilateral: all three sides are congruent (equal).
• Isosceles: exactly two sides are congruent.
• Scalene: no two sides are congruent.

Worked example

A triangle has side lengths

$$7\text{ cm},\quad 7\text{ cm},\quad 10\text{ cm}.$$

Step 1: Compare the side lengths.

The first two sides are both $7$ cm, so they are equal. The third side is $10$ cm, so it is different.

Step 2: Match the pattern.

There are exactly two equal sides.

Conclusion:

The triangle is isosceles.

Remember to use the labeled or measured side lengths, not how the triangle looks. This classification is based on sides, not on angles.