//chapter7
printf("\n");
Nmaxf1=2.5;
Nmaxf2=3.5;
Nmaxf3=1.5;//10^6*10^-6=1;
fcr1=sqrt(81*Nmaxf1);
fcr2=sqrt(81*Nmaxf2);
fcr3=sqrt(81*Nmaxf3);
printf("the critical frequencies are");
printf("\n %gHz %gHz %gHz",fcr1,fcr2,fcr3);