Conventionally we use uppercase letters to represent each apex, and lowercase letters to represent the angles.

The internal angles of a triangle will sum to 180°.

A regular triangle is called equilateral . All its sides will be of equal length and all its angles will be equal, i.e. all angles will be 60°

A triangle with two sides equal is called isosceles . It will also have two equal angles.

In a Right Angled triangle, the longest side is called the hypotenuse (alternatively, the side opposite the right angle).

Quick Quiz    

a) Find angles marked a and b

Isosceles Triangles

Quick Quiz    

a) Find the height of this isosceles triangle

Pythagoras's Theorem

The square of the hypotenuse equals the sum of squares of the other two sides

a2 = b2 + c2

Quick Quiz    

a) Find the length of the diagonal of the quadrilateral


The basic formula stated for the area of a triangle is

1/2 × base × height