View Compilation Error

0_0_18345592_9670.cpp: In function 'int main()':
0_0_18345592_9670.cpp:7:52: error: 'sqrt' was not declared in this scope
  t = sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2));
                                                    ^