Secant () is a trigonometric ratio. In a right triangle with an angle ,

is the side of the triangle that is part of angle , and is the side opposite the right angle.


The reciprocal of secant is cosine (abbreviated as ), while its inverse is or . Note that secant is not being raised to the power of -1; this is an inverse function, not a reciprocal.

The derivative of is , while its antiderivative is .

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