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23题即[3(a+1)+a-3]/(a²-1) *(a+1)/a
=4a/(a²-1) *(a+1)/a
=4/(a-1),代入a=√2+1
显然值为4/√2=2√2
24则是(x-y)(x+y)/(x-y)² *y/(x+y)+x/(x-y)
=y/(x-y)+x/(x-y)=(x+y)/(x-y)
代入x=1,y=2
式子的值为 -3
=4a/(a²-1) *(a+1)/a
=4/(a-1),代入a=√2+1
显然值为4/√2=2√2
24则是(x-y)(x+y)/(x-y)² *y/(x+y)+x/(x-y)
=y/(x-y)+x/(x-y)=(x+y)/(x-y)
代入x=1,y=2
式子的值为 -3
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