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Math Help - cosine equation

  1. #1
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    cosine equation

    Having a bit of a problem solving this


    cos2x = 3sinx +2



    thanks
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  2. #2
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    Quote Originally Posted by echo123 View Post
    Having a bit of a problem solving this


    cos2x = 3sinx +2



    thanks
    Substitute \cos(2x) = 1 - 2 \sin^2 x and re-arrange into a quadratic equation in sin x. Factorise. Use the null factor law. That should leave you with:

    (2 \sin x + 1) (\sin x + 1) = 0 \Rightarrow \sin x = - \frac{1}{2} \, or \, \sin x = -1.

    One difficult trig equation to solve becomes two simple trig equations to solve ......
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