赞 dinganglove 幼苗
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原式=1/(x+1)-(x+3)/(x+1)(x-1)×(x-1)²/(x+1)(x+3)
=(x+1)/(x+1)²-(x-1)/(x+1)²
=(x+1-x+1)/(x+1)²
=2/(x+1)²
=2/(-2+1)²
=2
=(x+1)/(x+1)²-(x-1)/(x+1)²
=(x+1-x+1)/(x+1)²
=2/(x+1)²
=2/(-2+1)²
=2
1年前
7
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