We have already seen which of the sides in a right-angled triangle is the hypotenuse.
If we have another angle indicated (like $\theta$θ in the diagram below) then we can also label the other two sides with two special names.
Opposite Side - is the name given to the side opposite the angle in question
Adjacent Side - is the name given to the side adjacent (next to) the angle in question.
Have a look at these triangles that I have named below. Note how the sides adjacent, opposite and hypotenuse are also abbreviated to A, O and H.
Let's have a look at these worked examples.
Which of the following is the opposite side to angle $\theta$θ?
Which of the following is the adjacent side to angle $\theta$θ?
A driver glances up at the top of a building.
True or false: According to the angle A, the height of the building is the opposite side.
True or false: According to the angle A, the distance from the driver to the building would be the opposite side.
Use trigonometric ratios and Pythagoras’ theorem in two and three dimensions
Apply geometric reasoning in solving problems
Apply right-angled triangles in solving measurement problems