Double Angle Identities

Key Questions

  • How do you use double angle identities to solve equations?

    Answer:

    As below.

    Explanation:

    Following table gives the double angle identities which can be used while solving the equations.

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    You can also have sin 2theta, cos 2theta expressed in terms of tan theta as under.

    sin 2theta = (2tan theta) / (1 + tan^2 theta)

    cos 2theta = (1 - tan^2 theta) / (1 + tan^2 theta)

    sankarankalyanam · 1 · Mar 9 2018
  • How do you use a double angle identity to find the exact value of each expression?

    You would need an expression to work with.

    For example:
    Given sinalpha=3/5 and cosalpha=-4/5, you could find sin2 alpha by using the double angle identity
    sin2 alpha=2sin alpha cos alpha.

    sin2 alpha=2(3/5)(-4/5)=-24/25.

    You could find cos2 alpha by using any of:
    cos2 alpha=cos^2 alpha -sin^2 alpha
    cos2 alpha=1 -2sin^2 alpha
    cos2 alpha=2cos^2 alpha -1

    In any case, you get cos alpha=7/25.

    Jim H · 1 · Mar 6 2015
  • What are Double Angle Identities?

    Double Angle Identities

    sin2theta=2sin theta cos theta

    cos2theta=cos^2theta-sin^2theta=2cos^2theta-1=1-2sin^2theta

    tan2theta={2tan theta}/{1-tan^2theta}

    I hope that this was helpful.

    Wataru · 1 · Nov 6 2014

Questions

Trigonometric Identities and Equations