Classifying Triangles by Their Sides

Year 7 Mathematics Understanding triangle types through side lengths

What Makes a Triangle?

A polygon with exactly three sides Three vertices (corners) where sides meet Three angles that always add up to 180° The most basic polygon in geometry

Think About It

Look around the classroom Can you spot any triangular shapes? What do you notice about their sides?

Three Ways to Classify Triangles

By their side lengths (today's focus) By their angle measures Both classifications can be used together We'll master side classification first

Triangle Classification by Sides

Equilateral Triangles

All three sides are equal in length All three angles are also equal (60° each) The most symmetrical triangle Example: sides of 5cm, 5cm, 5cm

Hands-On: Building Equilateral

Use rulers to draw a triangle Make all sides exactly 6cm long Check your angles with a protractor Compare with your partner's triangle

Isosceles Triangles

Exactly two sides are equal in length Two angles are also equal (base angles) Has a line of symmetry Example: sides of 7cm, 7cm, 4cm

Scalene Triangles

All three sides have different lengths All three angles are also different No lines of symmetry Example: sides of 3cm, 5cm, 7cm

Triangle Detective Challenge

Measure the sides of given triangles Classify each as equilateral, isosceles, or scalene Record your findings in the table Discuss your results with the class