# Triangles(KS2, Year 6)

## The Lesson

A triangle is a 2-dimensional shape with three sides and three angles. ## Dictionary Definition

The Oxford English Dictionary defines a triangle as "a figure (usually, a plane rectilineal figure) having three angles and three sides."

## Types of Triangle

There are different types of triangle. Triangles can be classified by lengths of sides or by angles.

## By Lengths of Sides

Triangles can be classified as equilateral, isosceles or scalene depending on whether 3, 2 or 0 side lengths and angles are equal. ## By Angles

Triangles can be classified as acute, obtuse or right triangles depending on whether all angles are acute (less than 90°), one angle is obtuse (more than 90°) or one angle is a right angle (90°). Read more about types of triangle

## Interactive Game on the Types of Triangle

Here is an interactive game to help you learn about the types of triangle.  ## Area of a Triangle

The area of a triangle is found using the formula: In this formula, b is the length of the base of the triangle and h is the height of the triangle.
Read more about how to find the area of a triangle

## Interior Angles of a Triangle

The interior angles of a triangle add up to 180°. Read more about the interior angles of a triangle

## Interactive Widget

Here is an interactive widget to help you learn about triangles.

## What's in a Name?

A triangle has three corners and so three angles. Just as a tricycle has three wheels, and a tripod has three legs, a shape with three angles in called a triangle. An alternative name for a triangle is a 'trigon', as it is a three-sided polygon. This is where we get the word trigonometry.

## Oblique Triangles

A triangle without a right angle is called an oblique triangle. Acute triangles and obtuse triangles are both oblique triangles. Help Us To Improve Mathematics Monster

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## See Also

Types of triangle Finding the area of a triangle The interior angles of a triangle Learn about triangles ( interactive widget)