Simple polar to cartesian conversion

1. Mar 4, 2008

Trousers

Find a Cartesian equation for the curve.
$$18=rcos \theta$$

$$\frac{\ 18}{cos \theta}= \sqrt{x^2+y^2}$$

how do I get rid of the cosine?

2. Mar 4, 2008

HallsofIvy

Staff Emeritus
Don't divide by it! What is $r cos(\theta)$ in terms of x and y coordinates? In other words, x= ? , y= ? in polar coordinates.

3. Mar 4, 2008

Trousers

x=18 is the solution. I can't believe it.