View Compilation Error

0_0_23043873_15183.cpp: In member function 'double Crane::getDistance(const Crane&) const':
0_0_23043873_15183.cpp:9:72: error: 'sqrt' was not declared in this scope
   return sqrt((x - crane.x)*(x - crane.x) + (y - crane.y)*(y - crane.y));
                                                                        ^