# 5.1: Right Triangle Trigonometry

- Page ID
- 1107

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A *right triangle* is defined as having one angle precisely equal to 90^{o} (a *right angle*).

##### Trigonometric Identities

H is the *Hypotenuse*, always being opposite the right angle. Relative to angle x, O is the *Opposite* and A is the *Adjacent*.

“Arc” functions such as “arcsin”, “arccos”, and “arctan” are the complements of normal trigonometric functions. These functions return an angle for a ratio input. For example, if the tangent of 45^{o} is equal to 1, then the “arctangent” (arctan) of 1 is 45^{o}. “Arc” functions are useful for finding angles in a right triangle if the side lengths are known.