Given that the circle C passes through point a (2, - 1), the center of the circle is on the line 2x + y = 0 and tangent to the line x + y = 0, then the standard equation of circle C is

Given that the circle C passes through point a (2, - 1), the center of the circle is on the line 2x + y = 0 and tangent to the line x + y = 0, then the standard equation of circle C is

Let C be (a, - 2A), then
|The distance from AC | = C to the line x + y = 0,
∴(a-2)^+(1-2a)^=a^/2,
5a^-8a+5=a^/2,
9A ^ - 16A + 10 = 0, no real root,
There is no solution to the problem