If the sum of the heights of transmitting and receiving antenna in LOS Communication is h . The range is maximum when the two antenna have a height hc,  then c is

Let r be the range of LOS between 2 antennas                           r=2RhT+2RhR   hT+hR=h    (according to data)           Let  hT=HSo         H+hR=h ⇒hR=h−H     Now,       r=2RH+2R(h−H) If r is max then  drdH=0                                       drdH=ddH(2RH+2R(h−H))                                   ⇒0=ddH2R[H+(h−H)] ⇒0=ddH[H+(h−H)] ⇒0=ddHH+ddH(h−H) ⇒0=12H−12(h−H) ⇒H=h−H ⇒2H=h ⇒H=h2