Đáp án:
`b)`
`\sqrt{21,8^2-18,2^2}`
`=\sqrt{(21,8-18,2).(21,8+18,2)`
`=\sqrt{3,6.40}`
`=\sqrt{144}`
`=12`
`d)`
`\sqrt{146,5^2-109,5^2+27.256}`
`=\sqrt{(146,5-109,5).(146,5+109,5)+27.256}`
`=\sqrt{37.256+27.256}`
`=\sqrt{256.(37+27)}`
`=\sqrt{256.64}`
`=\sqrt{256}.\sqrt{64}=16.8=128`
`b)`
`2\sqrt{2}.(\sqrt{3}-2)+(1+2\sqrt{2})^2-2\sqrt{6}=9`
`<=>2\sqrt{2}.\sqrt{3}-2\sqrt{2}.2+1+2.2\sqrt{2}+(2\sqrt{2})^2-2\sqrt{6}=9`
`<=>2\sqrt{6}-4\sqrt{2}+1+4\sqrt{2}+8-2\sqrt{6}=9`
`<=>(2\sqrt{6}-2\sqrt{6})+(4\sqrt{2}-4\sqrt{2})+(1+8)=9`
`<=>9=9(đpcm)`
Vậy `2\sqrt{2}.(\sqrt{3}-2)+(1+2\sqrt{2})^2-2\sqrt{6}=9`
