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Homework Help: Need some clarification in regards to trigonometry

  1. Jun 4, 2008 #1
    Need some clarification in regards to trigonometry....

    1. The problem statement, all variables and given/known data

    For some reason, I am not seeing the cause of this. In attached problem 1, the Forces of x are described with a cos while forces of y are described with sin. In the second problem, the forces of X use sin and the forces of y use cos...... What am I missing here? Is there a certain topic I can review? Is it because of the quadrants they are in? the triangle they make (I would think obviously, I just don't see it :( )


    Some of problem 1 has been cut off so I could attach the files

    2. Relevant equations

    How do I figure out if I'm suppose to use a cos or a sin for x or y?
     

    Attached Files:

  2. jcsd
  3. Jun 4, 2008 #2
    I can't see your images yet, but I'm going to guess the problem is which angle you are using:



    Consider a right angle triangle, with sides x, y and hypotenuse 1 (draw it!). Let's take the angle t to be between the sides x and 1: then cos(t)=adjacent/hypotenuse=x
    sin(t)=opposite/hypotenuse=y

    But if we take s to be the angle between 1 and y
    cos(s)=adjacent/hypotenuse=x
    sin(s)=opposite/hypotenuse=y

    Does that answer your question?
     
  4. Jun 5, 2008 #3

    tiny-tim

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    Homework Helper

    Hi r6mikey! :smile:

    Forget about triangles.

    The component in a direction is always found by multiplying by the cos of the angle between.

    (so you only use sin if it's the "wrong" angle! :biggrin: )
     
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