# Right-angled triangles

**Right-angled triangles**

The features of a** right-angled triangle** is as follows:

- It contains a right angle
- The longest side is called the hypotenuse
- The hypotenuse is also always opposite the right angle
- The sum of all angles in a triangle is always 180°
- Two angles which add up for 90° is called complementary angles.

**The opposite and adjacent sides**

The two shorter sides of a right-angled triangle have special naming terms. They are called in respect of the angle *x*:

- Adjacent side – the side between the angle and the right angle
- Opposite side – the side opposite the
*x*angle

**Similar right-angled triangles**

Two right-angled triangles with the same acute angle will be **similar** regardless of the length of the sides in comparison to one another.