The maximum distance between the transmitting and receiving antenna TV tower is D. If the heights of both towers are halved then maximum distance between them becomes

Initially ,  hT1=hT hR1=hR D1=D ∴D1=2RhT1+2RhR1  -------(1)  Finally ,  hT2=hT2 hR2=hR2 D2=?  ∴D2=2RhT2+2RhR2            =2RhT12+2RhR12           =2RhT12+2RhR12             =2RhT1+2RhR12              =D2                   [Using equation (1)]