(a+1/a方-a+4/1-a方)÷(a+3)(a-1)/a方+3a 其中a-2

=[(a+1)/a(a-1)-4/(a+1)(a-1)]×a(a+3)/(a+3)(a-1)
=(a²+2a+1-4a)/a(a+1)(a-1)×a/(a-1)
=(a-1)²/a(a+1)(a-1)×a/(a-1)
=1/(a+1)
当a=2时
原式=1/(2+1)=1/3