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Math Help - Solving for x

  1. #1
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    Solving for x

    Hey,

    I can't seem to do these 3 questions on my extension 1 assignment, hopefully sOmeone here can help.

    Solve for x, 0 < or = x < or = 360 give answers to nearest minute.
    1. 2cos(x+10)=-1
    2. 3(tanx)^2-7tanx+4=0

    3. Solve sin(2x-30)=sqrt[3]/2 for -180 < or = x < or = 180

    I'm abit confused, any help appreciated.

    Thanks,
    Last edited by Username; August 11th 2010 at 12:17 AM.
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  2. #2
    MHF Contributor Amer's Avatar
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    you should know that
    cos x = -1/2 when x = 120

    sin x = \sqrt{3}/2 when x = 60

    I will solve 1.
    2 \cos (x+10) = -1 \Rightarrow \cos (x+10) = \frac{-1}{2}

    10+x = 120 \Rightarrow x = 110

    second let tan x = y for example

    3y^2 - 7y +4 = 0 solve for y then x will equal arctan(y)

    third like the first one
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  3. #3
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    Quote Originally Posted by Amer View Post
    you should know that
    cos x = -1/2 when x = 120

    sin x = \sqrt{3}/2 when x = 60

    I will solve 1.
    2 \cos (x+10) = -1 \Rightarrow \cos (x+10) = \frac{-1}{2}

    10+x = 120 \Rightarrow x = 110

    second let tan x = y for example

    3y^2 - 7y +4 = 0 solve for y then x will equal arctan(y)

    third like the first one
    I got that answer except I need all possible values of x between 0 and 360, when I try to get the numbers, things go wrong =/
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  4. #4
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    solved all 3 problems, thanks.
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