四个坐标确定两条直线求这两条直线的交点坐标

1.项目的一个需求:如题
        //通过四个坐标点(x1,y1)与(x2,y2)连线  (x3,y3)与(x4,y4)连线
private function getPoint(x1:Number,y1:Number,x2:Number,y2:Number,x3:Number,y3:Number,x4:Number,y4:Number):Array{
var a:Number;  //交点x坐标
var b:Number;  //交点y坐标

var arr:Array = new Array();

var ysub12:Number = y1-y2;
var ysub34:Number = y3-y4;
var xsub12:Number = x1-x2;
var xsub34:Number = x3-x4;

a = ((x2*ysub12-y2*xsub12)*xsub34-(x4*ysub34-y4*xsub34)*xsub12)/(ysub12*xsub34-ysub34*xsub12);
b = (((a-x2)*ysub12)/xsub12)+y2;
arr.push(a);
arr.push(b);
trace(a,b);
            return arr;
}