Question

What is the standard equation for a circle with the center (2,1) and passing through (0, 1)

Answer 1

The radius is the distance from the center to any point.  The distance from (2,1) to (0,1) is of course 2.  The general formula for a circle with radius r and center (a,b) is

$(x-a)^2 + (y-b)^2 = r^2$

In our case we get

$(x-2)^2 + (y-1)^2 = 4$

Answer 2

So this is what I got (x-2)^2+(y-1)^2=4