الف) ${D_f} = ( - \infty , + \infty )\,\,\,,\,\,\,{D_g} = \left[ {2, + \infty } \right)$
${D_{gof}} = \left\{ {x \in {D_f}\left| {f(x) \in {D_g}} \right.} \right\} = \left\{ {x \in ( - \infty , + \infty )\left| {2x - 5 \geqslant 2} \right.} \right\} = \left[ {\frac{7}{2}, + \infty } \right)$
ب) $gof(x) = g(2x - 5) = \sqrt {2x - 5 - 2} = \sqrt {2x - 7} $