Đáp án:
`1. sqrt20-sqrt{6-2sqrt5}+\frac{5-2sqrt5}{sqrt5}`
`= 2sqrt5-sqrt{(1-sqrt5)^2}+\frac{(5-2sqrt5)sqrt5}{5}`
`= 2sqrt5-sqrt5+1+\frac{5sqrt5-10}{5}`
`= sqrt5+1+\frac{5(sqrt5-2)}{5}`
`= sqrt5+1+sqrt5-2`
`= 2sqrt5-1`
`2. sqrt{(2sqrt3-1)^2}-sqrt12`
`= 2sqrt3-1-2sqrt3`
`= -1`
`3. \frac{2}{sqrt2}+\frac{1}{sqrt3+sqrt2}+sqrt27`
`= sqrt2+sqrt3-sqrt2+3sqrt3`
`= 4sqrt3`