0_0_23845617_9184.cpp:10:18: error: 'acos' was not declared in this scope double pi=acos(-1); ^ 0_0_23845617_9184.cpp: In function 'int main()': 0_0_23845617_9184.cpp:27:37: error: 'atan2' was not declared in this scope double a=atan2(xx,yy); ^