化简求值，要过程 5
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（x²-2x/(x²-1)+[(x-1)-(2x-1)/(x+1)]
=x(x-2)/(x+1)(x-1)+[(x-1)(x+1)/(x+1)-(2x-1)/(x+1)]
=x(x-2)/(x+1)(x-1)+(x²-2x)/(x+1)
=x(x-2)/(x+1)(x-1)+x(x-2)(x-1)/(x+1)(x-1)
=[x(x-2)+x(x-2)(x-1)]/(x+1)(x-1)
=x²(x-2)/(x+1)（x-1)
当x=20/19时，
原式=[(20/19)²(20/19-2)]/[(20/19+1)(20/19-1)]
=-2400/247
=x(x-2)/(x+1)(x-1)+[(x-1)(x+1)/(x+1)-(2x-1)/(x+1)]
=x(x-2)/(x+1)(x-1)+(x²-2x)/(x+1)
=x(x-2)/(x+1)(x-1)+x(x-2)(x-1)/(x+1)(x-1)
=[x(x-2)+x(x-2)(x-1)]/(x+1)(x-1)
=x²(x-2)/(x+1)（x-1)
当x=20/19时，
原式=[(20/19)²(20/19-2)]/[(20/19+1)(20/19-1)]
=-2400/247
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