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.
Determine, through investigation , the relationship between the ratio of two sides in a right triangle and the ratio of the two corresponding sides in a similar right triangle, and define the sine, cosine, and tangent ratios