View Compilation Error

0_0_17060372_20.cpp: In function 'double dist(double, double, double, double)':
0_0_17060372_20.cpp:17:59: error: 'sqrt' was not declared in this scope
  return sqrt((x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2));
                                                           ^
0_0_17060372_20.cpp: In function 'double Area(double, double, double, Circle)':
0_0_17060372_20.cpp:24:32: error: 'fabs' was not declared in this scope
  else if(d <= fabs(radius - p.r)) return min(radius,p.r) * min(radius,p.r) * pi;
                                ^
0_0_17060372_20.cpp:26:74: error: 'acos' was not declared in this scope
  double a = acos((radius * radius + d * d - p.r * p.r) / (2 * radius * d));
                                                                          ^
0_0_17060372_20.cpp:28:65: error: 'sin' was not declared in this scope
  return radius * radius * a + p.r * p.r * b - radius * d * sin(a);
                                                                 ^