1.
3√20a+2√125a-√405a=3√(4*5a)+2√(25*5a)-√(81*5a)=6√5a+10√5a-9√5a=7√5a.
2.
(2√11-4√5)²=4*11-2*2*4*√(11*5)+16*5=44-16√55+80=124-16√55. (2)
3.
15-49a²=(√15)²-(7a)²=(√15-7a)(√15+7a) (4)
4.
8/√22=8*√22/(√22*√22)=8*√22/22=4*√22/11.
5.
(√6-2-√10)/(√3-√2-√5)=(√3*√2-√2*√2-√5*√2)*(√3-√2-√5)=
=√2*(√3-√2-√5)/(√3-√2-√5)=√2.