need help on solving the end of a calculus problem

Discussion in 'Community Discussion' started by macman2790, Mar 25, 2007.

  1. macman2790 macrumors 6502a

    macman2790

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    #1
    I'm using rolle's theorem which doesnt really matter.

    All i need to know is how to solve this:

    0 = 2*pi*cos(2*pi*x)

    I know it deals with an inverse cosine but i dont know how to manipulate it.

    thanks.
     
  2. plinden macrumors 68040

    plinden

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    #2
    I'm not going to tell you the answer, but you don't need to worry about the 2*pi multiplier, meaning you're looking for a value of x where cos(2*pi*x) = 0
     
  3. P-Worm macrumors 68020

    P-Worm

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    #3
    Instead of using an inverse cosine (which you still could, it would work), just think to yourself "What value does 2*Pi*x need to be to make the cosine of it equal to zero?"

    P-Worm
     
  4. GFLPraxis macrumors 604

    GFLPraxis

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    #4

    You've got three elements being multiplied here; 2, pi, and cos(2*pi*x).
    For the whole thing to be equal to zero, one of those three elements has to be zero, right? (since anything multiplied by zero is zero).

    2 can never be 0. Pi can never be zero. You know that 0 = cos(2*pi*x).

    What does X have to be for that to be zero?
     
  5. siurpeeman macrumors 603

    siurpeeman

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    #5
    or you could ask where cosine is equal to zero on the unit circle.
     
  6. cycocelica macrumors 68000

    cycocelica

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  7. siurpeeman macrumors 603

    siurpeeman

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    #7
    the x coordinate on the unit circle is a representation of cosine.
     

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  8. NightFlight macrumors 6502

    NightFlight

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    #8
    Oh sweet lord I hated calc. :(

    This makes my head hurt even just trying to remember.
     
  9. swiftaw macrumors 603

    swiftaw

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    #9
    Am I the only one who is confused about why this is referred to as a calculus problem?

    Algebra problem, yes. Trigonometry question, yes. Not sure there is any calculus here though.

    Edit: Re-reading the OP, I guess it was a calculus problem that yielded the final equation to be solved.

    cos(Y) = 0 when Y is an odd multiple of pi/2 that is when Y = (2i - 1)*pi/2 where i is any integer.

    thus in your problem cos(2*pi*x) = 0, x = (2i-1)/4 where i is any integer
     
  10. BurtonCCC macrumors 65816

    BurtonCCC

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  11. iSaint macrumors 603

    iSaint

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    #11
    I concur. :p
     
  12. Lunja macrumors 6502

    Lunja

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    Lincoln UK
    #12
    Nope, the answer's 42. It's the question that's wrong :cool:
     
  13. mkrishnan Moderator emeritus

    mkrishnan

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    #13
    Clearly you are confused, but not as confused as the person with the dog. ;)

    I'm guessing the OP had to solve this as part of a calculus problem. Of course this aspect is pretty purely trig.
     
  14. Abstract macrumors Penryn

    Abstract

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    #14
    How can you be doing calculus when you can't solve a very fundamental trigonometry problem?
     
  15. mkrishnan Moderator emeritus

    mkrishnan

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    #15
    No one said anything about doing calculus well. :eek:
     

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