Hello bradycat!

You can first use the mid-point formula to find the center of the circle:

midpoint formula says:

(x coordinate of center of circle)

and you do the same for your k (y coordinate) with the y coordinates of the given points.

So for your circle:

So the coordinate of the center of your circle are:

(h,k) or (-1,2)

Using that, see if you can figure out the standard form equation for the circle.

Good Luck!