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Homework Help: Need to solve thise 2 equations

  1. May 2, 2010 #1
    1. The problem statement, all variables and given/known data

    i have 2 equations:

    400cos [tex]\vartheta[/tex]a = 300 + Vacos45


    400sin [tex]\vartheta[/tex]a = Vasin45

    2. Relevant equations

    3. The attempt at a solution

    i have no clue, maybe square it.

  2. jcsd
  3. May 2, 2010 #2


    User Avatar
    Science Advisor
    Homework Helper

    Hi weedannycool! :wink:
    Yes, of course …

    what do you get? :smile:
  4. May 2, 2010 #3


    Staff: Mentor

    Also, you should replace cos45 and sin45 by sqrt(2)/2. I'm assuming the angles are in degrees.

    One other thing. Instead of starting a new thread for essentially the same (but corrected) problem, you should continue the old thread, putting in the corrected set of equations.
  5. May 3, 2010 #4
    right so i have the to equations squared. not positive with what i should to next though. is there a method for solving these.

    thanks for the help so far
  6. May 3, 2010 #5


    Staff: Mentor

    Do you know any identities involving the sum of the squares of the sine and cosine functions?
  7. May 3, 2010 #6
    Mark44's approach replacing sin45 and cos45 with sqrt(2)/2 seems the most straight forward approach. You have 2 equations with 2 unknowns, theta-a and Va. The expression with Va*sqrt(2)/2 in the second equation can be substituted into the first equation. You are left with one equation with one unknown, theta-a. Trial and error to find theta-a. Plug theta-a into either equation to find Va. Theta-a will be in degrees, Va won't be.
  8. May 3, 2010 #7
    thanks guys. relative motion is a blast.
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