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Homework Help: -.874=sin2θ θ=?

  1. Feb 19, 2009 #1
    BLAHH!!! I can't figure this one out!

    how do I isolate θ??

    Statement is...

    -0.874 = sin2θ


    jeeebuss can someone walk me through LOL! I need it to finish off a 4 hour physics question =/
     
  2. jcsd
  3. Feb 19, 2009 #2

    tiny-tim

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    Hi twenty5! :smile:

    walk this way … if x = sinθ, then θ = sin-1x (or arcsin x) :wink:
     
  4. Feb 19, 2009 #3
    so, if -0.874 = sin2θ

    then...
    sin-1(-0.874) = 2θ

    then...

    (sin-1(-0.874))/2 = θ?
     
  5. Feb 19, 2009 #4

    tiny-tim

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    Yes, except …

    i] it's normal to have only positive numbers inside the sin-1

    ii] you didn't say what the range of θ was … did they specify 0 < θ < π or 2π or what? … there may be several solutions, especially since you're divding the angle by 2 :wink:
     
  6. Feb 19, 2009 #5
    hmm not sure because I'm using this to do this... https://www.physicsforums.com/showthread.php?t=293717

    the very final post should be mine =P

    right, since the football player is kicking the ball above ground on a horizontal plane (straight field), and he is kicking it forward to a distance other than where he is standing, it has to be somewhere between 0o and 89o

    so, the answer I ended up with was -30.46o... so would that mean it is... wrong? LOL! omg... can't believe I spent 4 -5 hours to end up with a wrong answer -__- so depressing..
     
  7. Feb 19, 2009 #6

    tiny-tim

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    hmm … your minus sign seems to have come in post #18, but you don't show how you got it …

    yes, you need an answer between 0 and 90º, but your formula should give you two such answers.

    and i'm going to bed now … :zzz:​
     
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