Kinds of triangles

In your book, Maths Mela (Chapter 7, Shapes and Patterns), a rhombus (a shape with all sides equal) is cut into four triangle pieces. When two pieces are fitted together, they make new triangles. Measure their sides: each of these triangles has 2 equal sides. A triangle with 2 equal sides is called an isosceles triangle. Fold an isosceles triangle in half and you will see that it also has 2 equal angles.

A triangle with all 3 sides equal is an equilateral triangle. Fold it and check: all 3 of its angles are equal too.

Now cut an equilateral triangle in half, from one corner straight down to the middle of the opposite side. Each new triangle has 3 sides of different lengths: no two sides are equal. A triangle with no equal sides is called a scalene triangle, and it has no equal angles either.

So we can sort triangles by their sides. 2 equal sides: isosceles. 3 equal sides: equilateral. No equal sides: scalene. A triangle with sides 5 cm, 5 cm and 3 cm is isosceles; one with sides 4 cm, 6 cm and 7 cm is scalene.