ZJU-1090

 

三点共圆，求该圆面积。
胡推了半天发现证明了正弦定理。。。初中的东西了啊，真是好怀念
找出外心，算出和某点距离半径r，over 
//2008-01-03 22:32:13 Accepted 1090 C++ 00:00.00 396K #include<stdio.h> #include<math.h> #define pi 3.141592653589793 struct Point { double x; double y; }; double distance(Point a, Point b) { return sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y)); } int main() { Point A,B,C; freopen("1090.txt","r",stdin); double a,b,c,cosb,sinb; while(scanf("%lf%lf%lf%lf%lf%lf",&A.x,&A.y,&B.x,&B.y,&C.x,&C.y)!=EOF) { a=distance(B,C); b=distance(A,C); c=distance(B,A); cosb = (c*c+a*a-b*b)/(2.0*a*c); sinb = sqrt(1-cosb*cosb); printf("%.2lf/n",pi*b/sinb); } fclose(stdin); return 0; }