`a)3/\sqrt{3}-2/\sqrt{2}`
`=(3sqrt2)/(sqrt3sqrt2)-(2sqrt3)/(sqrt2sqrt3)`
`=(3sqrt2-2sqrt3)/(sqrt2.\sqrt3)`
`=(3sqrt2-2sqrt3)/(sqrt2.\sqrt3)`
`=(\sqrt3.sqrt3sqrt2-\sqrt2.sqrt2sqrt3)/(sqrt2.\sqrt3)`
`=(sqrt2.sqrt3(sqrt3-sqrt2))/(sqrt2.sqrt3)`
`=sqrt3-sqrt2`
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`b)1/(\sqrt{2}-1)+1/(\sqrt{2}+1)`
`=(\sqrt{2}+1)/[(\sqrt{2}-1)(\sqrt{2}+1)]+(\sqrt{2}-1)/[(\sqrt{2}+1)(\sqrt{2}-1)]`
`=\sqrt{2}+1+\sqrt{2}-1`
`=(\sqrt{2}+\sqrt2)+(1-1)`
`=2\sqrt{2}`
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`c)1/(5+2\sqrt{6})-1/(5-2\sqrt{6})`
`=(5-2\sqrt{6})/((5+2\sqrt{6})(5-2\sqrt{6}))-(5+2\sqrt{6})/[(5-2\sqrt{6})(5+2\sqrt{6})]`
`=5-2\sqrt{6}-5-2\sqrt{6}`
`=(5-5)-(2\sqrt6+2sqrt6)`
`=-4\sqrt6`
