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Homework Help: Very easy question

  1. Sep 30, 2007 #1
    sin-(cos(17pi/5))

    cos=(x+n2pi)=cos(x)

    I know that this becomes 7pi/5.. But what is substituted for the integer value? and why? (how does it become 7pi/5)
     
  2. jcsd
  3. Sep 30, 2007 #2
    because cosinus is periodic with period 2pi. So if you add 2pi in the argument you get the same result.
     
  4. Sep 30, 2007 #3

    HallsofIvy

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    Science Advisor

    It's not at all clear what you mean by "sin-(cos(17pi/5)". do you mean 'sine or cosine of that'? And, of course the "=" in "cos=" is a typo.

    17/5= 3 and 2/5= 2+ (1+ 2/5). The "n" in "n2pi" is 1 and the "x" is (1+ 2/5)pi= (7pi/5).
     
  5. Sep 30, 2007 #4

    HallsofIvy

    User Avatar
    Science Advisor

    It's not at all clear what you mean by "sin-(cos(17pi/5)". do you mean 'sine or cosine of that'? And, of course the "=" in "cos=" is a typo.

    17/5= 3+ 2/5= 2+ (1+ 2/5). The "n" in "n2pi" is 1 and the "x" is (1+ 2/5)pi= (7pi/5).
     
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