Homework Help: Need some clarification in regards to trigonometry

r6mikey · Jun 4, 2008

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?

fantispug · Jun 4, 2008

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?

tiny-tim · Jun 5, 2008

r6mikey said: ↑

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!

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! )

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Homework Help: Need some clarification in regards to trigonometry

r6mikey

Attached Files:

prob1.jpg

prob2.jpg

fantispug

tiny-tim