The trigonometric identities are a set of equations derived from the properties of the circle and the trigonometric functions. The identities are useful when manipulating and transforming expressions.

Name | Identity |
---|---|

Tangent Identity | |

Cotangent Identity | |

Pythagorean’s Identity | |

Sum of Two Angles (Sine) | |

Sum of Two Angles (Cosine) | |

Difference of Two Angles (Sine) | |

Difference of Two Angles (Cosine) | |

Double-Angle Identity (Sine) | |

Double-Angle Identity (Cosine) | |

Double-Angle Identity (Cosine 2) | |

Double-Angle Identity (Cosine 3) | |

Half-Angle Identity (Cosine) | |

Half-Angle Identity (Sine) |

The trig identities can be derived using the strategies outlined on these pages: