The terms "opposite" and "adjacent" are relative terms, which depend on a chosen one of the two non-right angles in a right triangle. So if the triangle is with the right angle at vertex , then if you are considering nonright angle/vertex , its opposite is the side not containing that vertex, so is side , while its adjacent is the other nonhypotenuse side which does contain the considered vertex .
Basically however the triangle is oriented, one imagines "standing" inside one of the angles, and looking "across" to the "opposite" (nonhypotenuse) for that angle, and the "adjacent" for that angle is the (nonhypotenuse) side one could touch from the place one is standing.
Note that neither opposite nor adjacent is ever the hypotenuse. The two could have the same length or not, and the terms still distinguish which is called which, based on the chosen non-right angle.
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