# Homework Help: General question

1. Mar 15, 2008

### Cursed

This isn't a problem, but I need help understanding this so I can do problems.

http://img255.imageshack.us/img255/3479/xythingat6.png [Broken]

So let's say...
1. This is part of the motion of a projectile
2. You're trying to find x and y

There are trig. identities that will give you x and y.

Example:
x = sin(36)*10
y = cos(36)*10

My question is... Which trig. identity/function do you use to solve for x, and why do you use that identity? Also explain the same thing for y. Please and thank you.

Last edited by a moderator: May 3, 2017
2. Mar 15, 2008

### mgb_phys

It's the basic defn of sin and cos.

Sin is the ratio of the opposite side over the hypotonuse
Cos is the ratio of the adjacent side over the hypotonuse

If you draw a line down to the X axis from the end of the slope (opposite the 36deg) you have a triangle.
The hypotonuse is 10units, the adjacent side is the distance in x and the opposite side (the exta line you just drew) the opposite side.

3. Mar 15, 2008

### Dick

And following mgb_phys' instructions you should find x=cos(36)*10 and y=sin(36)*10, the opposite of what you wrote.

Last edited: Mar 15, 2008
4. Mar 15, 2008

### Feldoh

$$sin x = \frac{opposite}{hypotenuse}$$

$$cos x = \frac{adjacent}{hypotenuse}$$

So applying that to your problem:

$$sin(36) = \frac{y}{10}$$

$$cos(36) = \frac{x}{10}$$

From there it's really straight forward for solving for x and y.