How We Classify Triangles

Triangles can be classified in various ways, including by their sides and angles. Here's an explanation of each classification.

By side lengths

Equilateral triangle: A triangle with three sides of equal length.

Isosceles triangle: A triangle with at least two sides of equal length.

Scalene triangle: A triangle with no sides of equal length.

By angle measures

Acute triangle: A triangle in which all three angles are acute angles (less than 90 degrees).

Right triangle: A triangle with one right angle (exactly 90 degrees).

Obtuse triangle: A triangle with one obtuse angle (greater than 90 degrees but less than 180 degrees).

Combining side lengths and angle measures

Equiangular triangle: A triangle in which all three angles are congruent (have the same measure).

Right isosceles triangle: A triangle that is both a right triangle and an isosceles triangle.

When classifying triangles, it's important to remember that the classifications are not mutually exclusive. For example, a triangle can be both isosceles and acute, or it can be scalene and obtuse.

To classify a triangle, examine its side lengths and angle measures. Measure the lengths of the sides using a ruler and use a protractor to measure the angles. Based on the measurements, determine which classification(s) apply to the triangle.

Understanding how to classify triangles helps students recognize patterns and relationships among geometric shapes, which is fundamental in geometry and can aid in problem-solving and reasoning skills.

Worksheets to practice classifying triangles

Across grade 4 – 6 math, we have increasingly difficult worksheets for students to practice classifying triangles.

Equilateral, isosceles, scalene and right triangles practice

In our grade 4 math section, students practice discerning equilateral, isosceles, scalene and right triangles from each other.

Classifying triangles worksheets

Grade 4 classifying angles worksheets

In these worksheets, students classify acute, obtuse and right angles.

Classifying triangles worksheets

Grade 5 classifying triangles worksheets

Students continue classifying triangles by equilateral, isosceles, scalene and right triangles.

Classifying triangles worksheets

Practice classifying angles

These grade 5 worksheets have students continue to practice acute, obtuse and right angles.

Classifying triangles at grade 6 level

These grade 6 worksheets have students practice classifying triangles as scalene, isosceles or equilateral.

Classifying angles worksheets

Students classify the angles, as well as measure them, in these grade 6 worksheets.

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