(a+1)/(a^2-a)+4/(1-a^2)
=(a+1)/(a^2-a)-4/(a^2-1)
=(a+1)/[a(a-1)]-4/[(a+1)(a-1)]
=[(a+1)^2-4a]/[a(a+1)(a-1)]
=(a-1)^2/[a(a+1)(a-1)]
=(a-1)/[a(a+1)]
(a^2+2a-3)/(a^2+3a)
=(a-1)(a+3)/[a(a+3)]
=(a-1)/a
所以原式={(a-1)/[a(a+1)]}/[(a-1)/a]
=[a(a-1)]/[a(a+1)(a-1)]
=1/(a+1)
=1/(-5/3+1)
=-3/2