Hypotenuse, Adjacent and Opposite Sides of a Right Triangle

Before we study trigonometry, we need to know how the sides of a right triangle are named. The three sides are called hypotenuse, adjacent and opposite sides.

In the following right triangle PQR,

• the side PQ, which is opposite to the right angle PRQ is called the hypotenuse. (The hypotenuse is the longest side of the right triangle.)
• the side RQ is called the adjacent side of angle θ .
• the side PR is called the opposite side of angle θ .

Note: The adjacent and the opposite sides depend on the angle θ . For complementary angle of θ , the labels of the 2 sides are reversed.

Example:

Identify the hypotenuse, adjacent side and opposite side in the following triangle:

a) for angle x

b) for angle y

Solution:

a) For angle x: AB is the hypotenuse, AC is the adjacent side , and BC is the opposite side.

b) For angle y: AB is the hypotenuse, BC is the adjacent side , and AC is the opposite side.

Videos

Opposite Sides, Adjacent Sides and Hypotenuse of a Right Triangle.
Definition of Cos, Sin, Tan, Csc, Sec, Cot

The first part of this video will explain the diffremce between the hypotenuse, adjacent and opposite sides of a right triangle.

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