1/2=1/1*2=1/1-1/2,1/6=1/2*3=1/2-1/3,1/12=1/3*4=1/3-1/4. 計算1/(x-2)(x-3)-2/(x-1)(x-3)+1/(x-1)(x-2)

1/2=1/1*2=1/1-1/2,1/6=1/2*3=1/2-1/3,1/12=1/3*4=1/3-1/4. 計算1/(x-2)(x-3)-2/(x-1)(x-3)+1/(x-1)(x-2)

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