大双人舞

下面程序的输出结果是 【15】 。
#include ＜iostream.h＞
#include ＜math.h＞
class point double x;
double y;
public:
point(double a, double b) x=a;
y=b;

friend double distance(point a, point b) ;
;
double distance(point a, point b) return sqrt ((a. x-b.x) * (a. x-b.x)+ (a. y-b. y) * (a. y-b. y) );void main() point p1(1,2);
point p2(5,2);
cout＜＜distance(p1,p2)＜＜end1;