//chapter 7
printf("\n");
ht=150;
hr=2;
Is=9;
d=40*10^3;
f=1.2*10^6;
c=3*10^8;
lamda=c/f;
printf("the wavelength is %dm",lamda);
E=120*(%pi)*ht*hr*Is/(lamda*d);
printf("\nthe electric field is %gV/m",E);