If you write:
$\displaystyle \sqrt{(h_t+h_r)^2+d^2}$ as $\displaystyle \sqrt{d^2\cdot\left(\frac{(h_t+h_r)^2}{d^2}+1 \right)}= ...$
Can you complete? ...
For the other term it's similar.
take the square root of d^2 [(ht+hr)^2 / d^2 + 1], this whole term is underneath a square root...
(d^2 [(ht+hr)^2 / d^2 + 1])^1/2 = d [(ht+hr)^2 / d^2 + 1]^1/2
take the square root of d^2 [(ht+hr)^2 / d^2 + 1], this whole term is underneath a square root...
(d^2 [(ht+hr)^2 / d^2 + 1])^1/2 = d [(ht+hr)^2 / d^2 + 1]^1/2