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Math Help - What is the value of cos(pi + 301pi/2)

  1. #1
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    What is the value of cos(pi + 301pi/2)

    I have to make a video explaining this problem, sent by the person who hired me, but it doesn't appear to be correct.

    What is the value of cos( + 301/2)?
    A.-1/2
    B. 1
    C. 0
    D. 1/2
    E 3/2



    This is the solution given:


    cos(+301/2) = cos(+75*2+ /2)= cos(+ /2)
    = 0
    Ans: C


    When I use degrees = radians * 180/pi, that answer isn't correct. And when I plug in the original cos (pi+301pi/2) into google calculator, it isn't 0.


    Am I missing something?
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  2. #2
    Behold, the power of SARDINES!
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    Quote Originally Posted by fcabanski View Post
    I have to make a video explaining this problem, sent by the person who hired me, but it doesn't appear to be correct.

    What is the value of cos( + 301/2)?
    A.-1/2
    B. 1
    C. 0
    D. 1/2
    E 3/2



    This is the solution given:


    cos(+301/2) = cos(+75*2+ /2)= cos(+ /2)
    = 0
    Ans: C


    When I use degrees = radians * 180/pi, that answer isn't correct. And when I plug in the original cos (pi+301pi/2) into google calculator, it isn't 0.


    Am I missing something?
    I assume you mean what is in the title?? not the ??

    \cos\left(\pi+ \frac{301\pi}{2}\right)=\cos\left(\frac{303\pi}{2} \right)

    Now cosine is a perioidic function with a period of two pi i.e

    \cos(2\pi n +x)=\cos(x) where n is any integer.

    so \frac{303\pi}{2}=151\pi +\frac{\pi}{2}=150\pi +\frac{3}{2}\pi=2\pi (75)+\frac{3\pi}{2}

    so finally we get

    \cos \left( 150\pi +\frac{3\pi}{2}\right) =\cos \left(\frac{3\pi}{2}\right)=0
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  3. #3
    A riddle wrapped in an enigma
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    Quote Originally Posted by fcabanski View Post


    When I use degrees = radians * 180/pi, that answer isn't correct. And when I plug in the original cos (pi+301pi/2) into google calculator, it isn't 0.


    Am I missing something?
    Try this with your calculator.

    \frac{301\pi}{2}\cdot\frac{180}{\pi}=27090 degrees.

    \cos\left(\pi+\frac{301\pi}{2}\right)\Longrightarr  ow \cos(180+27090)=0
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  4. #4
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    Thanks.

    I know your explanation is correct. However, why does Google calculator get it wrong when I enter:

    cos (pi+301pi/2)?

    "Try this with your calculator."

    cos (27270 degrees) != 0
    Last edited by fcabanski; June 2nd 2009 at 12:49 PM.
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  5. #5
    MHF Contributor Amer's Avatar
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    the answer is ZERO

    see

    What is the value of cos(pi + 301pi/2)-right.jpg
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