# Function

A function is a relation that uniquely associates members of one set with members of another set. The term "function" is sometimes implicitly understood to mean continuous function, linear function, or function into the complex numbers.

Function is a high school-level concept that would be first encountered in a pre-calculus course covering functions. It is an Advanced Placement Calculus AB topic and is listed in the California State Standards for Grade 7.

### Examples

Cosine: | The cosine is the ratio of the length of an angle's adjacent side to the length of the hypotenuse in a right triangle. |

Exponential Function: | The exponential function is the function consisting of the base of the natural logarithm e taken to the power of a given variable. |

Gamma Function: | The gamma function is an extension of the factorial to real and complex arguments. |

Polynomial: | A polynomial is a mathematical expression involving a sum of powers in one or more variables multiplied by coefficients. |

Power: | In arithmetic, a power is an exponent to which a given quantity is raised. |

Rational Function: | A rational function is a function that can be written as the quotient of two polynomials. |

Riemann Zeta Function: | The Riemann zeta function is a special function of mathematics and physics that is intimately related to deep results surrounding the prime number theorem. |

Sine: | The sine is the ratio of the length of a given angle's opposite side to the length of the hypotenuse in a right triangle. |

Tangent: | (1) In trigonometry, the tangent of an angle is the ratio of the length of a given angle's opposite side to the length of the angle's adjacent side in a right triangle. (2) In geometry, two figures are said to be tangent to one another if they "just touch". |