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Math Help - Trig Identity/Pre-Calc help

  1. #1
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    Trig Identity/Pre-Calc help

    I have a problem as follows:

    cos((π/3) - X)

    I then used the addition identity of cos(x-y) = cos x cos y + sin x sin y and got:

    cos(π/3)*cosX + sin(π/3)*sinX

    Then i used the unit circle to get

    (1/2)*cosX + √(3)*sinX

    And am now stuck. I'm supposed to solve for 'x' but i'm not sure how to continue.
    Help please?
    -I'm supposed to use trig identities, of course.

    I posted this in both urgent hw help and pre-calc because its both urgent and in pre-calc . I'll remove one as soon as either get a reply.
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  2. #2
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    Dear Dust,

    what is your problem?? You wrote a simple expression not an equation or else.

    Bye the way, once again how many sin(pi/3) ?
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  3. #3
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    I have to solve for x. Thats the problem - I don't know how to further simplify to the point where i can solve X.

    And .. just one pi/three? I don't understand your question; sorry.

    Its just cos of (pi/3) minus the variable x
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  4. #4
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    Quote Originally Posted by Dust View Post

    cos(π/3)*cosX + sin(π/3)*sinX

    (1/2)*cosX + √(3)*sinX
    There is an error above

    it should be
    \frac{1}{2}cos(x) + \frac{\sqrt{3}}{2}Sin(x) = \frac{cos(x) +\sqrt{3}Sin(x)}{2}

    maybe that's why you got stuck

    Last edited by fonso_gfx; December 18th 2008 at 05:59 PM.
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  5. #5
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    solve, solve, but what??
    You wrote an expression: cos(pi/3 - x) without sign '='.
    Man can usually solve an equation, e. g. 2x = 10
    but only 2x is meaningless to solve.

    My question: sin(pi/3) = ?
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  6. #6
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    Skalkaz - the point of this problem is to solve for x. so the problem equals whatever x is. But you don't know it till you solve it so it doesn't really matter.

    Thank you, Fonso.
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  7. #7
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    How do you continue solving this problem?
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  8. #8
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    No problem.
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  9. #9
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    Quote Originally Posted by Dust View Post
    Skalkaz - the point of this problem is to solve for x. so the problem equals whatever x is. But you don't know it till you solve it so it doesn't really matter.

    Thank you, Fonso.
    Skalkaz is exactly right, you can't solve an equation for x without an equation.

    You have given the left hand side

    \cos{(\frac{\pi}{3} - x)}

    Now you need an equals sign and a right hand side.

    Then we can solve.
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