八年级下册数学分式1/(a-1)(a-2)+1/(a-2)(a-3)+1(a-3)(a-4)+.+1(a-9)(a-10)结果是多少

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八年级下册数学分式1/(a-1)(a-2)+1/(a-2)(a-3)+1(a-3)(a-4)+.+1(a-9)(a-10)结果是多少八年级下册数学分式1/(a-1)(a-2)+1/(a-2)(a-3)

八年级下册数学分式1/(a-1)(a-2)+1/(a-2)(a-3)+1(a-3)(a-4)+.+1(a-9)(a-10)结果是多少
八年级下册数学分式1/(a-1)(a-2)+1/(a-2)(a-3)+1(a-3)(a-4)+.+1(a-9)(a-10)结果是多少

八年级下册数学分式1/(a-1)(a-2)+1/(a-2)(a-3)+1(a-3)(a-4)+.+1(a-9)(a-10)结果是多少
1/(a-1)(a-2)+1/(a-2)(a-3)+1(a-3)(a-4)+.+1(a-9)(a-10)
=1/(a-2)-1/(a-1)+1/(a-3)-1/(a-2)+.1/(a-10)-1/(a-9)
=1/(a-10)-1/(a-1)
=9/(a-10)(a-1)

用裂项相消啊!1/(a-1)-1/(a-10)

原式=1/(a-10)-1/(a-1)
1/(a-1)(a-2)=1/(a-2)-1/(a-1)
1/(a-2)(a-3)=1/(a-3)-1/(a-2)……
这样一次类推就可以消去中间各项得出结果

观察发现{1/(a-1)(a-2)}=1/(a-2)-1/(a-1);后面的也有相同的规律,也就是说原式等于1/(a-2)-1/(a-1)+1/(a-3)-1/(a-2)+......+1/(a-10)-1/(a-9),这样一来,1/(a-2)一直到1/(a-9)都是由一个正有一个负,相互抵消,最后结果就是1/(a-10)-1/(a-1).