17 18 两题

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17 18 两题
 

17半个.
18 (3x+4)/(x-1)(x+1)-2(x+1)/(x-1)(x+1)*(x-1)2/(x+2)
=(3x+4-2x-2)/(x-1)(x+1)*(x-1)2/(x+2)
=(x+2)/(x-1)(x+1)*(x-1)2/(x+2)
=(x-1)/(x+1)
=(-3-1)/(-3+1)
=-4/-2
=2
童鞋给个采纳