题目

    Every human being has a unique arrangement of the skin on his fingers and this arrangement is unchangeable. Scientists and experts have proved the uniqueness of finger-prints and discovered that no exactly similar pattern is passed on from parents to children, though nobody knows why this is the case. The ridge structure on a person’s fingers does not change with growth and is not affected by surface injuries. Burns, cuts and other damage to the outer part of the skin will be replaced in time by new one, which bears a reproduction of the original pattern. It is only when the inner ski7．在平面直角坐标系中，A（1，-1），B（1，3），点C在直线x-y+1=0上．（1）若直线AC的斜率是直线BC的斜率的2倍，求直线AC的方程；（2）点B关于y轴对称点为D，若以DC为直径的圆M过点A，求C的坐标．