Solution 3 (c).

Solution.  Let    be the angle of inclination of the line   .   The slope of the line is    and  

                    .
                    
Therefore

                    .  

We are done.   

Aside.  We can let Mathematica double check our work.

So that    .

We are really done.   

Aside.  We can explore some graphs.

                    The image of the circle     under the mapping   

                        is the line        that passes through the origin.   

This solution is complements of the authors.

(c) 2008 John H. Mathews, Russell W. Howell