How to Identify Triangles in Geometry

Equilateral triangles have three sides of equal length.

Triangles in geometry are identified based on the degree measure of their angles and the relative lengths of their sides. Triangles are classified by their angles as acute, right or obtuse, and by their sides as scalene, isoceles or equilateral. Identify a triangle by measuring its angles and sides using a protractor and a ruler.

Things You'll Need

• Protractor
• Ruler

Instructions

1. Measure each of the three angles of the triangle using a protractor. Identify the triangles as acute if all angles are less than 90 degrees, right if one measures 90 degrees and obtuse if one measures more than 90 degrees.

2. Identify the triangle as an acute triangle only if all three of the angles are acute. Identify the triangle as a right triangle only if it has a right angle. Identify the triangle as an obtuse triangle only if it has an obtuse angle. Triangles cannot have more than one right or obtuse angle because the sum of the three angles is always 180 degrees.

3. Use a ruler to measure the three sides of the triangle, using consistent units, such as centimeters or feet.

4. Identify the triangle as scalene only if each of the three sides is a different length. Identify the triangle as isoceles only if two sides have the same length and the other has a different length. Identify the triangle as equilateral if all three sides are the same length.

5. Identify the triangle with its side classification first, then its angle classification. For example, refer to an isoceles right triangle, not a right isoceles triangle.

References

• Math.com: Classifying Angles
• Math.com: Triangles -- First Glance