View Compilation Error

0_0_36534754_21229.cpp: In member function 'void Geometry::Vector2::rotate(Geometry::FLOAT_, bool)':
0_0_36534754_21229.cpp:268:49: error: 'M_PI' was not declared in this scope
             theta = (use_degree ? theta / 180 * M_PI : theta);
                                                 ^