View Compilation Error

0_0_31847378_12228.cpp: In function 'int main(int, char**)':
0_0_31847378_12228.cpp:13:25: error: 'atan' was not declared in this scope
   v = 1 / tan(atan(1 / s) - atan(1 / u));
                         ^
0_0_31847378_12228.cpp:13:40: error: 'tan' was not declared in this scope
   v = 1 / tan(atan(1 / s) - atan(1 / u));
                                        ^