View Compilation Error

0_0_32035742_17660.cpp: In function 'int main()':
0_0_32035742_17660.cpp:14:53: error: 'sqrt' was not declared in this scope
   t = sqrt((x1 - x2)*(x1 - x2) + (y1 - y2)*(y1 - y2));
                                                     ^