View Compilation Error

0_0_33642543_2670.cpp: In function 'double F(double)':
0_0_33642543_2670.cpp:8:39: error: 'sqrt' was not declared in this scope
  return 2 * B * sqrt(1 - x / A * x / A);
                                       ^
0_0_33642543_2670.cpp: In function 'double get_ans(double, double, double)':
0_0_33642543_2670.cpp:19:30: error: 'fabs' was not declared in this scope
  if (fabs(l_ans + r_ans - ans) <= eps) return ans;
                              ^