Cosine is the ratio of the adjacent side to the hypotenuse in a right triangle. In the unit circle, it's the x-coordinate of a point on the circle.

Cotangent is the reciprocal of tangent. It's the ratio of cosine to sine (or adjacent to opposite in a right triangle, cot = 1/tan).

Cosecant is the reciprocal of sine. It's the ratio of the hypotenuse to the opposite side in a right triangle (csc = 1/sin).

Secant is the reciprocal of cosine. It's the ratio of the hypotenuse to the adjacent side in a right triangle (sec = 1/cos).

Sine is the ratio of the opposite side to the hypotenuse in a right triangle. In the unit circle, it's the y-coordinate of a point on the circle.

Tangent is the ratio of sine to cosine (or opposite to adjacent in a right triangle). It represents the slope of the line from the origin to a point on the unit circle.

Arccosine (arccos) is the inverse function of cosine. It returns the angle (in the selected units) whose cosine equals the input ratio. The input must be between -1 and 1. The output angle will be in the range [0°, 180°] for degrees or [0, π] for radians.

Arcsine (arcsin) is the inverse function of sine. It returns the angle (in the selected units) whose sine equals the input ratio. The input must be between -1 and 1. The output angle will be in the range [-90°, 90°] for degrees or [-π/2, π/2] for radians.

Arctangent (arctan) is the inverse function of tangent. It returns the angle (in the selected units) whose tangent equals the input ratio. Unlike arcsin and arccos, arctan accepts any real number as input. The output angle will be in the range (-90°, 90°) for degrees or (-π/2, π/2) for radians.

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