`a) 2/(sqrt{3}-1)+2/(sqrt{3}+1)-(3-sqrt{3})/(sqrt{3}-1)`
`=(2(sqrt{3}+1))/(3-1)+(2(sqrt{3}-1))/(3-1)-(sqrt{3}(sqrt{3}-1))/(sqrt{3}-1)`
`=sqrt{3}+1+sqrt{3}-1-sqrt{3}`
`=sqrt{3}`
`b) ((sqrt{14}-sqrt{7})/(1-sqrt{2})+(sqrt{15}-sqrt{5})/(1-sqrt{3})):1/(sqrt{7}-sqrt{5})`
`=((sqrt{7}(sqrt{2}-1))/(1-sqrt{2})+(sqrt{5}(sqrt{3}-1))/(1-sqrt{3})).(sqrt{7}-sqrt{5})`
`=(-sqrt{7}-sqrt{5}).(sqrt{7}-sqrt{5})`
`=-(sqrt{7}+sqrt{5})(sqrt{7}-sqrt{5})`
`=-(7-5)`
`=-2`
