1/X²+3X+2 +1/X²+5X+6 +1/X²+7X+12 +1/X²+9X+20

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1/X²+3X+2+1/X²+5X+6+1/X²+7X+12+1/X²+9X+201/X²+3X+2+1/X²+5X+6+1/X²

1/X²+3X+2 +1/X²+5X+6 +1/X²+7X+12 +1/X²+9X+20
1/X²+3X+2 +1/X²+5X+6 +1/X²+7X+12 +1/X²+9X+20

1/X²+3X+2 +1/X²+5X+6 +1/X²+7X+12 +1/X²+9X+20
原式= 1/(x+1)(x+2) + 1/(x+2)(x+3) + 1/(x+3)(x+4) + 1/(x+4)(x+5)
= (x+3+x+1) / [ (x+1)(x+2)(x+3) ] + (x+5+x+3) / [ (x+3)(x+4)(x+5)]
= 2 / [(x+1)(x+3)] + 2/ [(x+3)(x+5)]
= [2(x+5)+2(x+1)] / [ (x+1)(x+3)(x+5)]
= (4x+12) / [ (x+1)(x+3)(x+5)]
= 4 / [ (x+1)(x+5)]

1/X²+3X+2 +1/X²+5X+6 +1/X²+7X+12 +1/X²+9X+20
=1/(x+1)(x+2)+1/(x+2)(x+3)+1/(x+3)(x+4)+1/(x+4)(x+5)
=1/(x+1)-1/(x+2)+1/(x+2)-1/(x+3)+1/(x+3)-1/(x+4)+1/(x+4)-1/(x+5)
=1/(x+1)-1/(x+5)
=4/(x+1)(x+5)