Simple polar to cartesian conversion

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