/in/foo.c: In function 'main':
/in/foo.c:5:22: warning: implicit declaration of function 'sqrt' [-Wimplicit-function-declaration]
 printf("%lf\n%lf",l/(sqrt(3))/v/(sqrt(3)/2),v*l/(sqrt(3))/v/(sqrt(3)/2));
                      ^~~~
/in/foo.c:5:22: warning: incompatible implicit declaration of built-in function 'sqrt'
/in/foo.c:5:22: note: include '<math.h>' or provide a declaration of 'sqrt'