# Solving trigonometric system of equations

1. Sep 8, 2010

### Alibeg

Hi. I'd like to know whether is it possible to do the following, and if so, how...(and also, whether is it possible to solve similar problems)

I have parametric equation of a curve and I need to find its intersection with a ray that starts at the origin of the coordinate system and makes known angle with the positive x-axis.

Curve:
x = ( R-r )( cos($$\varphi$$) - cos($$\theta$$) ) + D cos($$\varphi$$ (R-r)/r - $$\theta$$ (R-r)/r )
y = ( R-r )( sin($$\varphi$$) - sin($$\theta$$) ) + D sin($$\varphi$$ (R-r)/r - $$\theta$$ (R-r)/r )

R, r and D are known constants.

Ray:
y = tan($$\beta$$) x

$$\beta$$, $$\theta$$ and $$\varphi$$ are angles, $$\varphi$$ is my parameter, $$\theta$$ and $$\beta$$ are some variable angles.

I need to find the coordinates of the intersection of curve and the ray as a function of $$\theta$$ and $$\beta$$.

In short I want to know coordinates of intersection but without the parameter $$\varphi$$ in them.

2. Sep 8, 2010

### Alibeg

This is the picture of my problem for r = 5, R= 6 and D = 7.
Note that $$\theta$$ is not visible on this picture, but it had a fixed value while I was taking the picture.
Making $$\theta$$ change would cause curve to change position and orientation.

Thanks :D

3. Sep 8, 2010

### jackmell

How about numerically? It's not too hard to design an algorithm that zeros into the roots without having to manually select starting values.

4. Sep 9, 2010

### Alibeg

Hmmm. I need distance of that intersection from the origin of the coordinate system. But I need it as a function of a $$\theta$$ so I can find its minimal value for different $$\theta$$s . (i would have to use derivatives and other tricks later)

5. Sep 9, 2010

### jackmell

Well what, that ain't no hill neither. But first you need to make clear if you are wiling to settle for a numeric approximation. If not, then I can't do it.

Last edited: Sep 9, 2010
6. Sep 10, 2010

### Alibeg

I am sorry, but numeric solution doesn't help me, since I cannot analyze the data further that way, and I also don't think it's an easy task.

Maybe I am using a wrong approach.

Here more description of my problem:
I have to change $$\theta$$ from 0 to some value. While changing it my (green) curve moves (the origin of the coordinate system is always inside of it).
If I trace my curve, I get a unusual white shaped area. I want to find the equation for the boundary line of that area.