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  1. Wikipedia
    https://en.wikipedia.org/wiki/List_of_trigonometric_identities

    List of trigonometric identities - Wikipedia

    • In trigonometry, trigonometric identities are equalities that involve trigonometric functions and are true for every value of the occurring variables for which both sides of the equality are defined. Geometrically, these are identities involving certain functions of one or more angles. They are distinct from triangle identities, which are identities potentially involving angles b… See more

    Reflections, shifts, and periodicity

    By examining the unit circle, one can establish the following properties of the trigonometric functions.
    When the direction of a Euclidean vector is represented by an angle this is the angle determine… See more

    Angle sum and difference identities

    These are also known as the angle addition and subtraction theorems (or formulae).
    The angle difference identities for and can be derived from the angle sum versions by substituting for and using the facts that and . They can al… See more

    Multiple-angle and half-angle formulae

    Formulae for twice an angle.
    Formulae for triple angles.
    Formulae for multiple angles.
    The Chebyshev method is a recursive algorithm for finding the nth multiple angle formula kn… See more

    What was the first use of Delta Pi?
    The first recorded use is Oughtred's"δ.π{\displaystyle \delta .\pi }", to express the ratio of periphery and diameter in the 1647 and later editions of Clavis Mathematicae.
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    Table of Contents
    Reflections, shifts, and periodicity
    Angle sum and difference identities
    Multiple-angle and half-angle formulae
    What was the first use of Delta Pi?
     
  1. Symbolab
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  3. Wikipedia
    https://en.wikipedia.org/wiki/List_of_formulae_involving_Ď€

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  4. Calculator Pi
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  5. Wolfram MathWorld
    https://mathworld.wolfram.com/PiFormulas.html

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  7. Math is Fun
    https://www.mathsisfun.com/numbers/pi

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  8. Brilliant
    https://brilliant.org/wiki/pi

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  9. Mathway
    https://www.mathway.com/popular-problems/Trigonometry/328635

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  10. Wikipedia
    https://en.wikipedia.org/wiki/Pi

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