A circle with its center on the line $y = 3x$ in the 1^st quadrant is tangent to the y-axis.    

1. If the radius is $2$, what is the equation of the circle?

   Hint (a):

   Try sketching the circle. The circle to the right has a radius of 2. Try placing it on the axis so it matches the circle described in the problem. The line y = 3x has been graphed for you.

   Answer (a):

   Use the coordinates of the center and the radius to write an equation in general form.
   $\left(x − 2\right)^{2} + \left(y − 6\right)^{2} = 4$

2. If the radius is $3$, what is the equation of the circle?

   Hint (b):

   See part (a).

   Answer (b):

   $\left(x − 3\right)^{2} + \left(y − 9\right)^{2} = 9$