Đáp án + Giải thích các bước giải:
`a)` `(sqrt10-sqrt15+3sqrt5)*sqrt5-sqrt72`
`=sqrt10*sqrt5-sqrt15*sqrt5+3sqrt5*sqrt5-sqrt72`
`=sqrt50-sqrt75+3*5-sqrt72`
`=5sqrt2-5sqrt3+15-6sqrt2`
`=-sqrt2-5sqrt3+15`
`b)` `(15sqrt50+5sqrt200-3sqrt450):8sqrt10`
`=(15*5sqrt2+5*10sqrt2-3*15sqrt2):(8*sqrt5*sqrt2)`
`=(15*5sqrt2)/(8*sqrt5*sqrt2)+(5*10sqrt2)/(8*sqrt5*sqrt2)-(3*15sqrt2)/(8*sqrt5*sqrt2)`
`=(75sqrt2)/(8sqrt5*sqrt2)+(50sqrt2)/(8sqrt5*sqrt2)-(45sqrt2)/(8sqrt5*sqrt2)`
`=75/(8sqrt5)+50/(8sqrt5)-45/(8sqrt5)`
`=(75+50-45)/(8sqrt5)=80/(8sqrt5)`
`=(8*10)/(8sqrt5)=10/(sqrt5)=(10sqrt5)/5=2sqrt5`.
