圆的一些操作

1、三点求圆心坐标和半径：

x0=((y2-y1)(y3*y3-y1*y1+x3*x3-x1*x1)-(y3-y1)(y2*y2-y1*y1+x2*x2-x1*x1))/(2.0*((x3-x1)(y2-y1)-(x2-x1)(y3-y1)));

y0=((x2-x1)(x3*x3-x1*x1+y3*y3-y1*y1)-(x3-x1)(x2*x2-x1*x1+y2*y2-y1*y1))/(2.0*((y3-y1)(x2-x1)-(y2-y1)(x3-x1)));

r^2=(x1-x0)(x1-x0)+(y1-y0)(y1-y0);