Triangles are polygons with three sides.

- A
**right − angled**triangle contains an angle of 90**°**.e.g. A = 90

^{o } - An
**obtuse − angled**triangle contains an angle between 90**°**and 180**°**.

- A
**scalene**triangle contains three sides unequal in length. All angle sizes are different. - An
**isosceles**triangle is one in which two of the sides and their opposite angles are equal.

**Symmetry of Triangles**

An isosceles triangle has **one** axis of symmetry.

axis of symmetry

e.g. sides: a = b

angles: A = B

An **equilateral triangle** is one in which all three sides are of equal length and each interior angle is 60**°**.

An equilateral traingle has **three** axes of symmetry.

e.g. sides: a = b = c

### Properties of Triangles

- The interior angles of a triangle always add up to 180
**°**. - An exterior angle of a triangle is equal to the sum of the two opposite interior angles.
- The exterior angles of a triangle always add up to 360
**°**. - The smallest angle of a triangle is opposite the smallest side.
- The largest angle of a triangle is opposite the largest side.
w = x + y

Click here to test your knowledge of the properties of quadrilaterals and triangles.