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Math Help - Help Me with trigs please

  1. #1
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    Help Me with trigs please

    I have a test tomrow and i cant do some of the problems on the topic please help. i want to know how to do these before my test tomrow

    express sin 320degrees as a sin function of a positive acute angle

    find the value of cos^2 x - 2cos x= 0

    thx
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  2. #2
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    Quote Originally Posted by madfreshx View Post
    I have a test tomrow and i cant do some of the problems on the topic please help. i want to know how to do these before my test tomrow

    express sin 320degrees as a sin function of a positive acute angle

    find the value of cos^2 x - 2cos x= 0

    thx
    \sin(320) = -\sin(40)

    320 degrees is 40 degrees below the (+) x-axis



    \cos^2{x} - 2\cos{x}= 0

    factor out \cos{x} ...

    \cos{x}(\cos{x} - 2) = 0

    \cos{x} = 0 at x = \frac{\pi}{2} and x = \frac{3\pi}{2}

    \cos{x} = 2 has no solution.
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  3. #3
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    thank you very much
    can you also help me with this
    sinx = - 1/2 solve for x in neareast degree of 0 equal or greater than x equal or greater 360

    also for the second question you asnwered for me i made a mistake
    it is deta not x
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  4. #4
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    Quote Originally Posted by madfreshx View Post
    thank you very much
    can you also help me with this
    sinx = - 1/2 solve for x in neareast degree of 0 equal or greater than x equal or greater 360

    also for the second question you asnwered for me i made a mistake
    it is deta not x

    theta , not deta ... so, change all the x's to theta's
     \sin{\theta} = -\frac{1}{2}

    this value is on your unit circle in quad III and IV ...

    \theta = 210^{\circ} and \theta = 330^{\circ}

    next time start a new thread for a new question.
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