\(6,\\ a,A=\left(\sqrt{x}-\sqrt{y}\right)\left(\sqrt{x}+\sqrt{y}\right)-3\left(\sqrt{x}+\sqrt{y}\right)=\left(\sqrt{x}+\sqrt{y}\right)\left(\sqrt{x}-\sqrt{y}-3\right)\\ b,B=\left(\sqrt{x}\right)^2-2\cdot2\sqrt{x}+2^2=\left(\sqrt{x}-2\right)^2\)
\(c,C=\left(\sqrt{x}-\sqrt{y}\right)\left(x+\sqrt{xy}+y\right)+\sqrt{xy}\left(\sqrt{x}-\sqrt{y}\right)=\left(\sqrt{x}-\sqrt{y}\right)\left(x+2\sqrt{xy}+y\right)=\left(\sqrt{x}-\sqrt{y}\right)\left(\sqrt{x}+\sqrt{y}\right)^2\\ d,D=5x^2-5x\sqrt{y}-2x\sqrt{y}+2y=5x\left(x-\sqrt{y}\right)-2\sqrt{y}\left(x-\sqrt{y}\right)=\left(5x-2\sqrt{y}\right)\left(x-\sqrt{y}\right)\)
