# When and how do you know which is side is the adjacent vs opposite in a right triangle?

In trigonometry, the hypotenuse is always the longest side but, the adjacent and opposite sides are not as consistent. When and how do you know which is side is the adjacent vs. opposite in a right triangle? In this diagram, when is seven on the opposite side? When does it become adjacent?

Bonus: To find side AB would I use Tan (19˚): 7/x = 7 tan (19˚)?

• This is always with respect to the marked angle given. The way I teach it - start from the vertex where the angle is and "look" out towards a side - that side is the opposite side. Nov 4, 2021 at 1:40
• @SeanRoberson Thank you for your explanation. So the 7 is on the opposite side (of the angle), correct? There were times while doing problems, that side was considered adjacent and it threw me off because I did not understand why. Nov 4, 2021 at 1:45
• In the figure, side $AC$ (of length $7$) is opposite angle $B$ (the $19^\circ$ angle) but adjacent to angle $C$ (the $71^\circ$ angle). Side $AB$ is opposite angle $C$ and is adjacent to angle $B.$ Nov 4, 2021 at 3:08
• @DavidK Thank you, Mr. David K. Nov 4, 2021 at 3:16