计算几何AngRadVector

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db Ang(db x){return(x*180.0/pi);}
db Rad(db x){return(x*pi/180.0);}
V Rotate(V A,db a){return V(A.x*cos(a)-A.y*sin(a),A.x*sin(a)+A.y*cos(a));}
db Cross(V A,V B){return A.x*B.y-A.y*B.x;}
int main(){
  cout<<Ang(2*pi)<<endl;
  D A(3,0),B(0,4);
  cout<<Cross(A,B)<<endl;
  cout<<Cross(B,A)<<endl;
  cout<<"Rad(90)="<<Rad(90)<<endl;
  cout<<"Ang(Rad(90))="<<Ang(Rad(90))<<endl;  
  cout<<A.x<<" "<<A.y<<endl;
  A=Rotate(A,Rad(90));
  cout<<A.x<<" "<<A.y<<endl;
  return 0;
}