Hướng dẫn trả lời:
`Q = 2sqrt{45} + sqrt{5} - 3sqrt{80}`
`= 2sqrt{9cdot5} + sqrt{5} - 3sqrt{16cdot5}`
`= 2sqrt{3^2cdot5} + sqrt{5} - 3sqrt{4^2cdot5}`
`= 2cdot3sqrt{5} + sqrt{5} - 3cdot4sqrt{5}`
`= 6sqrt{5} + sqrt{5} - 12sqrt{5}`
`= -5sqrt{5}`
`A = sqrt{(2 - sqrt{3})^2} + 2sqrt{3}`
`= |2 - sqrt{3}| + 2sqrt{3}`
`= (2 - sqrt{3}) + 2sqrt{3}` (Vì `2 = sqrt{4} > sqrt{3}`)
`= 2 - sqrt{3} + 2sqrt{3}`
`= 2 + sqrt{3}`
`B = sqrt{18} - 2sqrt{50} + 3sqrt{8} + 3`
`= sqrt{9cdot2} - 2sqrt{25cdot2} + 3sqrt{4cdot2} + 3`
`= sqrt{3^2cdot2} - 2sqrt{5^2cdot2} + 3sqrt{2^2cdot2} + 3`
`= 3sqrt{2} - 2cdot5sqrt{2} + 3cdot2sqrt{2} + 3`
`= 3sqrt{2} - 10sqrt{2} + 6sqrt{2} + 3`
`= 3 + (3sqrt{2} - 10sqrt{2} + 6sqrt{2})`
`= 3 - sqrt{2}`
Đáp án:
`Q = -5sqrt{5}`
`A = 2 + sqrt{3}`
`B = 3 - sqrt{2}`
