# 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

__Facts__

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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