Right-angled Triangles

A right-angled triangle is a triangle with one of its angles 90°_. In a right-angled triangle, the side opposite the right angle, which is the longest side in the triangle, is called the hypotenuse. 

Hypotenuse: The longest side is called the hypotenuse. It is the side opposite the right angle.

Opposite: This is the side opposite the angle under consideration. 

Adjacent: It is the side next or adjacent to the angle you are using.