原式＝{[(a+1)/2(a-1)]-3/[2(a+1)(a-1)]-(a+3)/[2(a+1)]}*4(a+1)(a-1)/3
={[(a+1)^2-3-[(a+3)(a-1)]/[2(a+1)(a-1)]}*4(a+1)(a-1)/3
={[a^2+2a+1-3-a^2-2a+3]/[2(a+1)(a-1)]}*4(a+1)(a-1)/3
=1/[2(a+1)(a-1)]*4(a+1)(a-1)/3
=2/3
我把答案写在纸上，发给你，你等一下哦
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