a=(√3-√2)(√2-1)=√6-2-√3+√2
1/a=1/(√3-√2)(√2-1)=(√3+2√)(√2+1)=√6+2+√3+√2
(a^2-1)/2a
=1/2(a-1/a)
=1/2(√6-2-√3+√2-√6-2-√3-√2)
=1/2(-4-2√3)
=-2-√3
2a/(1-a^2)
=1/(-2-√3)
=(-2+√3)/(4-3)
=-2+√3