解ï¼è§ä¸å¾ï¼a^2+b^2=r^2+(a-x)^2+(b-y)^2=r^2+a^2-2ax+x^2+b^2-2by+y^2=0;
æ´çï¼å¾ï¼r^2-ax-by=0; y=ax/b-r^2/b; x>0æ¶ï¼çå¼ä¸çx,y为åç¹åæ ï¼yæ两个å¼ï¼y>0åy<0; è¦æ»¡è¶³è¿ä¸æ¡ä»¶ã
y=+/-(ax/b-r^2/b); é£ä¹ï¼å线çæç为ï¼k=+/-a/bã