Obtaining equation of circles

Question

Find the equation of a circle tangent to both x and y axes passing through (-2,1) and

also

Find the equation of another circle with center (5,3) and tangent to the x axis only.

Answer 1

For the first question:
Using the fact that $(-2,1)$ is in the second quadrant, the circle is of the form $(x+r)^2+(y-r)^2 = r^2$.

For the second question:
The circle is of the form $(x-5)^2+(y-3)^2=r^2$.