(x+2/x-2-x-2/x+2)-x2/x2-4

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(x+2/x-2-x-2/x+2)-x2/x2-4
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(x+2/x-2-x-2/x+2)-x2/x2-4
(x+2/x-2-x-2/x+2)-x2/x2-4

(x+2/x-2-x-2/x+2)-x2/x2-4
=[(x+2)²-(x-2)²]/(x+2)(x-2)-x²/(x+2)(x-2)
=(x+2+x-2)(x+2-x+2)/(x+2)(x-2)-x²/(x+2)(x-2)
=4x/(x+2)(x-2)-x²/(x+2)(x-2)
=-(x²-4x)/(x²-4)

通分得出=[(x+2)^2-(x-2)^2-x^2]/(x^2-4)=(4x-x^2)/(x^2-4)