Find the equation of the circle that is tangent to the line x-1=0 and x-6=0, and passes through the point (2,2).

since our two lines are parallel, the circle's diameter must be 6-1=5 (and so r=5/2) 
This means that the x-coordinate of the center must 1+5/2=7/2 
Next we can write: 
 
after solving we determine that k=0. 
therefore...