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Math Help - Double Angle Identities

  1. #1
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    Double Angle Identities

    Use an identity to write each expression as a trig function value or as a single number.

    1-2sin^2(22 1/2 degrees)


    and

    1/4 - 1/2 sin^2 (47.1 degrees)

    Thanks for reading!
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  2. #2
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    Hello Thatoneguy12345
    Quote Originally Posted by Thatoneguy12345 View Post
    Use an identity to write each expression as a trig function value or as a single number.

    1-2sin^2(22 1/2 degrees)


    and

    1/4 - 1/2 sin^2 (47.1 degrees)

    Thanks for reading!
    These both use the identity \cos2\theta =1-2\sin^2\theta

    1) 1-2\sin^222\tfrac12^o=\cos 45^o=\frac{1}{\sqrt2}

    2) \tfrac14-\tfrac12\sin^247.1^o=\tfrac14(1-2\sin^247.1^o)=\tfrac14\cos 94.2^o, and you can't simplify this any further.

    Grandad
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  3. #3
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    wait for the first one, how did you get cos45?

    I begin with 1 - 2 sin ^ 2 (22 1/2) and I end up multiplying the 22 with 1/2 and getting 11. So I end up with 1-2sin^2 11. Is that the correct step?

    NVM I get it! Thanks a lot
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