Đáp án:
`a)(sqrt8-3sqrt2)*sqrt2`
`=(2sqrt2-3sqrt2)*sqrt2`
`=-sqrt2*sqrt2`
`=-2`
`b)(sqrt{14}-sqrt7)/(1-sqrt2)`
`=(sqrt7(sqrt2-1))/(-(sqrt2-1))`
`=-sqrt7`
`2a)sqrt{19+sqrt{136}}-sqrt{19-sqrt{136}}`
`=sqrt{19+2sqrt{34}}-sqrt{19-2sqrt{34}}`
`=sqrt{17+2sqrt{34}+2}-sqrt{17-2sqrt{34}+2}`
`=sqrt{(sqrt{17}+sqrt2)^2}-sqrt{(sqrt{17}-sqrt2)^2}`
`=sqrt{17}+sqrt2-(sqrt{17}-sqrt2)`
`=2sqrt2`