P 1P2 is a chord, and the midline of the chord passes through the center of the circle, so the equation of the midline of P 1P2 is solved.

The midpoint of P 1P2 is (1, -2), the slope is -4/-2 = 2, and the slope of the vertical line is-1/2.

∴ The equation of the midline is y+2=- 1/2*(x- 1).

Simultaneous y=-x, x=3, y=-3.

The center coordinate is (3, -3).

The distance from the center of the circle to P 1 is √( 1+9)=√ 10, that is, the radius is √ 10.

Solution 2:

Let the center coordinate be (t, -t)

The distance formula is √[(t-2)? +t？ ]=√[t？ +(t-4)？ ], the solution is t=3.

∴ The center coordinate is (3, -3)

Solutions with the same radius 1