1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    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

    User Avatar
    Staff Emeritus
    Science Advisor

    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

    User Avatar
    Staff Emeritus
    Science Advisor

    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

    User Avatar
    Science Advisor
    Homework Helper

    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
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Trigonometry Help
  1. Trigonometry help (Replies: 7)

Loading...