4.1Classifying Triangles
Quick Answer
By sides: scalene (no equal sides), isosceles (at least two equal sides), equilateral (all three equal). By angles: acute (all angles < 90°), right (one 90° angle), obtuse (one angle > 90°), equiangular (all 60°).
Essential Question
How do we classify triangles by their sides and angles, and can a triangle belong to more than one classification?
Learning Goals
- 1Classify triangles by side lengths.
- 2Classify triangles by angle measures.
- 3Apply both classifications simultaneously.
- 4Use the Triangle Angle Sum Theorem to find missing angles.
Key Vocabulary
Scalene triangle
A triangle with no congruent sides.
Isosceles triangle
A triangle with at least two congruent sides.
Equilateral triangle
A triangle with all three sides congruent.
Acute triangle
A triangle with all three angles less than 90°.
Right triangle
A triangle with exactly one 90° angle.
Obtuse triangle
A triangle with one angle greater than 90°.
Equiangular triangle
A triangle with all three angles equal to 60°; always equilateral.
Full lesson content coming soon
Worked examples, guided practice problems, a workbook, quiz, and downloadable PDF resources will be added to this lesson in Phase 2. The learning goals and vocabulary above reflect the complete lesson scope.