Need some clarification in regards to trigonometry

  • Thread starter r6mikey
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  • #1
r6mikey
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Need some clarification in regards to trigonometry...

Homework Statement



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

Homework Equations



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

Attachments

  • prob1.jpg
    prob1.jpg
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  • prob2.jpg
    prob2.jpg
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Answers and Replies

  • #2
fantispug
105
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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?
 
  • #3
tiny-tim
Science Advisor
Homework Helper
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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

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

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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