Bài 4:
`a) sqrt{8} + sqrt{18} - 6sqrt{1/2} - sqrt{200}`
`= 2sqrt{2} + 3sqrt{2} - sqrt{(6^{2})/2} - 10sqrt{2}`
`= 2sqrt{2} + 3sqrt{2} - 3sqrt{2} - 10sqrt{2}`
`= -8sqrt{2}`
`b) 3/(2)sqrt{6} + 2sqrt{2/3} - 4sqrt{3/2}`
`= (3\sqrt{6})/2 + (2\sqrt{6})/3 - 2sqrt{6}`
`= (3/2 + 2/3 - 2)sqrt{6}`
`= (\sqrt{6})/6`
`c) 6sqrt{8/9} - 5sqrt{32/25} + 14sqrt{18/49}`
`= 4sqrt{2} - 4sqrt{2} + 6sqrt{2}`
`= 6sqrt{2}`
`d) 2sqrt{16/3} - 3sqrt{1/27} - 6sqrt{4/75}`
`= (8\sqrt{3})/3 - (\sqrt{3})/3 - (4\sqrt{3})/5`
`= sqrt{3}(8/3 - 1/3 - 4/5)`
`= (23\sqrt{3})/15`
Bài 6:
`a) (20sqrt{12} - 15sqrt{27}) : 5sqrt{3}`
`= (24 - 27).5sqrt{3} : 5sqrt{3}`
`= -3`
`b) (sqrt{75} + sqrt{243} - sqrt{48}) : sqrt{3}`
`= (5 + 9 - 4).sqrt{3} : sqrt{3}`
`= 10`
`c) (sqrt{2} + 1)^2 + (sqrt{2} - 1)^2`
`= 2 + 2sqrt{2} + 1 + 2 - 2sqrt{2} + 1`
`= 6`
`d)``(sqrt{28} - 2sqrt{3} + sqrt{7}).sqrt{7} + sqrt{84}`
`= 14 - 2sqrt{21} + 7 + 2sqrt{21}`
`= 21`
