1.根号5-根号6-根号20+根号(2/3)+根号(5/9)
=根号5-根号6-2*根号5+(根号6)/3+(根号5)/3
=-2/3(根号5+根号6)
2.a根号(1/a)+根号4b-根号a/2-b根号(1/b)
=根号a+2根号b-根号a/2-根号b
=根号a/2+根号b