[latex]a) f(x) = cfrac{2 + x}{sqrt{x}}\\ x extgreater 0\\ D=(0, +infty)\\ b) f(x) = cfrac{sqrt{x - 2}}{x - 3}\\ x-2 geq 0wedge x eq3\\ x geq 2wedge x eq3\\ D=langle2, 3)cup(3,+infty)\\ c) f(x) = sqrt{x + 1} - 5\\ x+1 geq 0\\ x geq -1\\ D=langle-1,+infty)[/latex]