Hướng dẫn trả lời:
`A = 2sqrt{2} - sqrt{50} + 2sqrt{8} - sqrt{98}`
`= 2sqrt{2} - sqrt{25cdot2} + 2sqrt{4cdot2} - sqrt{49cdot2}`
`= 2sqrt{2} - sqrt{5^2cdot2} + 2sqrt{2^2cdot2} - sqrt{7^2cdot2}`
`= 2sqrt{2} - 5sqrt{2} + 2cdot2sqrt{2} - 7sqrt{2}`
`= 2sqrt{2} - 5sqrt{2} + 4sqrt{2} - 7sqrt{2}`
`= - 6sqrt{2}`
`B = 3cdot sqrt{1/3} + 1/2cdot sqrt{12} + sqrt{3}`
`= sqrt{3^2cdot1/3} + 1/2cdot sqrt{4cdot3} + sqrt{3}`
`= sqrt{9cdot1/3} + 1/2cdot sqrt{2^2cdot3} + sqrt{3}`
`= sqrt{9/3} + 1/2cdot2sqrt{3} + sqrt{3}`
`= sqrt{3} + sqrt{3} + sqrt{3}`
`= 3sqrt{3}`
`C = ({2 + sqrt{2}}/{1 + sqrt{2}} + {3sqrt{3}}/{sqrt3}) - 1 ÷ 1/{sqrt{2} + sqrt{3}}`
`= ({sqrt{2}cdot(sqrt{2} + 1)}/{1 + sqrt{2}} + {3cdot sqrt{3}}/{1cdot sqrt3}) - 1 cdot {sqrt{2} + sqrt{3}}/1`
`= ({sqrt{2}cdot(1 + sqrt{2})}/{1 + sqrt{2}} + 3) - 1 cdot (sqrt{2} + sqrt{3})`
`= (sqrt{2} + 3) - (sqrt{2} + sqrt{3})`
`= sqrt{2} + 3 - sqrt{2} - sqrt{3}`
`= (sqrt{2} - sqrt{2}) + (3 - sqrt{3})`
`= 3 - sqrt{3}`
Đáp án:
`A = - 6sqrt{2}`
`B = 3sqrt{3}`
`C = 3 - sqrt{3}`
