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Trigonometry Help

  1. Sep 9, 2007 #1
    I've been really stumped by this one from my math class. It's a two variable trig. question with two equations. I believe there simultaneous but I'm not sure

    3 = 1.2(cosx) + v(cos30)
    0 = 1.2(sinx) - v(sin30)

    Solve for the values of x & v

    Please explain how you got your answer or show work. Thanks
     
  2. jcsd
  3. Sep 9, 2007 #2

    arildno

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    Well, solve for v first from, say, the 2nd eq.
    Then you get a trig equation; use the summation formula to reshape it so that you can solve for relevant x's
     
  4. Sep 9, 2007 #3
    Sorry I'm not familar with the summation formula. I solved for V in the second equation and got V = .6sinx.

    I substituted that into the second equation and got sin = 0, 180 or 360 but then the 2nd equation doesn't check out. I know I'm doing it wrong somehow just not sure how
     
  5. Sep 9, 2007 #4

    HallsofIvy

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    Actually, I suspect the problem asked YOU to explain how you got your answer or shiow work. I don't have to! Let x= cos(x) and y= sin(x). then you have the two equations
    3= 1.2x+ vy and 0 = 1.2x+ vy as well as the obvious equation [itex] x^2+ y^2= 1[/itex]. What happens if you add the first two equations?
     
  6. Sep 9, 2007 #5
    HallsofIvy how do you get those equations?

    Seems it should be
    [tex]
    3 = 1.2x + v\frac{\sqrt{3}}{2}[/tex]
    [tex]0 = 1.2y - 0.5v[/tex]
    [tex]x^2 + y^2 = 1
    [/tex]
     
  7. Sep 9, 2007 #6

    HallsofIvy

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    How did I get those two equations? I copied them from the first post in this thread!
    3 = 1.2(cosx) + v(cos30)
    0 = 1.2(sinx) - v(sin30)
    I now see, looking more closely, that it might be good idea to multiply the first equation by sin(30) and the second equation by cos(30). Although it wasn't said, I assume that is "30 degrees" so that cos(30)= [itex]\sqrt{2}/3[/itex] and sin(30)= 1/2.
     
  8. Sep 9, 2007 #7

    AlephZero

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    That's the right idea, but the solution to 0 = 1.2(sinx) - v(sin30) = 1.2(sinx) -v(0.5) isn't v = 0.6 sin x.
     
  9. Sep 9, 2007 #8
    i just solved it, long prob
     
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