Naming sides of right angled triangles

Here we are going to look at how to name the sides of right angled triangles before we look at the ratios of the lengths of sides of similar right angled triangles.

From the point of view of the red angle, angle BAC, the side BC is called the opposite. This makes sense as BC is opposite the red angle.

Side AC is next to, or adjacent to, the red angle. This side is called the adjacent when we are talking about the red angle.

Side AB is, of course, the hypotenuse no matter which angle we are talking about because it is the longest side of a right angled triangle.

From the point of view of the green angle, angle ABC, the side AC is the opposite and the side BC is the adjacent.

Often the names Opposite, Hypotenuse and Adjacent are abbreviated to O, H and A.