Maths – Triangle

The triangle is a 2D (flat) shape that has three straight sides and three vertices (corners). The three angles of a triangle always add up to 180 degrees.

Maths – Triangle


Triangles are named according to their sides or angles.

The following triangles are named according to their sides:

  • Equilateral Triangle – All three sides are the same (equal) length.
  • Isosceles Triangle – Has two or more sides that are of equal length (Therefore, an equilateral triangle can also be an isosceles triangle).
  • Scalene Triangle – None of its sides are the same length.

The following triangles are names according to their angles:

  • Right-angled Triangle – The largest of its three angles is a right angle (90 degrees).
  • Acute-angled Triangle – The largest of its three angles is an acute angle (less than 90 degrees).
  • Obtuse-angled Triangle – The largest of its three angles is an obtuse angle (more than 90 degrees).

Good to know!

Triangles are extremely useful. Measuring objects using triangles is called trigonometry. Modern computers usually use triangles to make complex graphic images or shapes.

Learning resources

Example questions

  • Tell me the definition of a circle.
  • What does ‘diameter’ mean?
  • What is an arc?
  • What is a chord?
  • Tell me a fun fact about circles.
  • What is the name of a triangle whose sides are all of equal length?
  • What makes a triangle a scalene triangle?
  • Tell me about the angles in an acute-angled triangle.
  • What is the process of measuring using triangles called?
  • Other than the circle and the triangle, name two geometric plane shapes.

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