先化简,再求值（3a/a-1 - a/a+1)*a^2-1/a,其中a=根号2-2
问题描述：
先化简,再求值（3a/a-1 - a/a+1)*a^2-1/a,其中a=根号2-2
答
[3a/(a-1) - a/(a+1)]*(a^2-1)/a=a[3/(a-1) - 1/(a+1)]*(a^2-1)/a=[3/(a-1) - 1/(a+1)]*(a^2-1)=[3(a+1)-(a-1)]/[(a-1)(a+1)]*(a^2-1)=[3a+3-a+1]/(a^2-1)*(a^2-1)=3a+3-a+1=3a-a+1+3=2a+4=2(√2-2)+4=2√2-4+4=2√2...