Như sau :
\(D=\frac{\left(x+2\right)\left(x+3\right)+x\sqrt{\left(3-x\right)\left(3+x\right)}}{x\left(3-x\right)+\left(x+2\right)\sqrt{\left(3-x\right)\left(3+x\right)}}=\frac{\sqrt{x+3}\left[\left(x+2\right)\sqrt{x+3}+x\sqrt{3-x}\right]}{\sqrt{3-x}\left(x\sqrt{3-x}+\left(x+2\right)\sqrt{3+x}\right)}=\frac{\sqrt{x+3}}{\sqrt{3-x}}\)