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Math Help - Finding zeroes for trig functions

  1. #1
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    Finding zeroes for trig functions

    When you have functions like these:

    y=sinx+cos2x
    or
    y=-sinx-4cos2x

    How can I determine the zeroes? Is there an identity for cos2x that could be useful in factoring a term out, or etc?
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by theowne View Post
    When you have functions like these:

    y=sinx+cos2x
    or
    y=-sinx-4cos2x

    How can I determine the zeroes? Is there an identity for cos2x that could be useful in factoring a term out, or etc?
    write \cos 2x as 1 - 2 \sin^2 x. then your equations break down into quadratic equations in \sin x. It is easy to find the zeros from there
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