View Compilation Error

0_0_35584994_3360.cpp: In function 'void graph()':
0_0_35584994_3360.cpp:93:83: error: 'sqrt' was not declared in this scope
             if(spd[i]*ti>=sqrt((x[i]-x2[j])*(x[i]-x2[j])+(y[i]-y2[j])*(y[i]-y2[j]))){
                                                                                   ^