View Compilation Error

0_0_29470067_106.cpp: In function 'void Get_mat(double, double, double, double)':
0_0_29470067_106.cpp:4:19: error: 'cos' was not declared in this scope
     double c=cos(a);
                   ^
0_0_29470067_106.cpp:5:19: error: 'sin' was not declared in this scope
     double s=sin(a);
                   ^