Giải:
a) [tex]3-\sqrt{3}+\sqrt{15}-3\sqrt{5}=3(1-\sqrt{5})-\sqrt{3}(1-\sqrt{5})=\sqrt{3}(1-\sqrt{5})(\sqrt{3}-1)[/tex]
b) [tex]\sqrt{1-a}(1-\sqrt{1+a})[/tex] (Với [tex]-1< a< 1[/tex] )
c) [tex]\sqrt{a^3}-\sqrt{b^3}+\sqrt{a^2b}-\sqrt{ab^2}=a\sqrt{a}-b\sqrt{b}+a\sqrt{b}-b\sqrt{a}=a(\sqrt{a}+\sqrt{b})-b(\sqrt{a}+\sqrt{b})=(\sqrt{a}+\sqrt{b})(\sqrt{a}-\sqrt{b})(\sqrt{a}+\sqrt{b})=(\sqrt{a}+\sqrt{b})^2(\sqrt{a}-\sqrt{b})[/tex]
d) [tex]x-y+\sqrt{xy^2}-\sqrt{y^3}=x-y+y\sqrt{x}-y\sqrt{y}=(\sqrt{x}-\sqrt{y})(\sqrt{x}+\sqrt{y})+y(\sqrt{x}-\sqrt{y})=(\sqrt{x}-\sqrt{y})(\sqrt{x}+\sqrt{y}+y)[/tex]