//chapter 2
printf("\n");
f=2*10^9;
c=3*10^8;
lamda=c/f;
printf("the wavelngth is %gm",lamda);
//part b
Pr=10^-12;
Gt=200;
Gr=200;
d=3*10^6;
Pt=((4*(%pi)*d)/lamda)^2*(Pr/(Gt*Gr));
printf("\nthe transmitted power is %gW",Pt);