1/(√2-1)=1/(√2-1) . (√2+1)/(√2+1)=1.(√2+1)/((√2-1)(√2+1))=
=(√2+1)/(2-1)=√2+1
(√7+√3)(√7-√3)=7-3=4
3√12.4√8=3.4.√(12.8)=12√96=12√(4.24)=12√(4.4.6)=
=12√(16.6)=12.4.√6=48√6
20√18:5√2)=20√(9.2):5√2=20.3.√2:5√2=12
5√6(√6-√3)=5√6.√6-5√6.√3=5.6-√(6.3)=
=30-√18=30-√(9.2)=30-3√2
3√5.(1+2√5)=3√5+6.5=3√5+30
(5√2)ˇ25:(5√2)ˇ23=(5√2)ˇ(25-23)=(5√2)²=5².(√2)²=25.2=50