数学题 急求解！！！
(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)...
(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)
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正解：
(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)
=(1+1/2+1/3+1/4)*(1/2+1/3+1/4)+1/5*(1+1/2+1/3+1/4)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)
=1/5*(1+1/2+1/3+1/4)-1/5*(1/2+1/3+1/4)
=1/5
(1+1/2+1/3+1/4)*(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)
=(1+1/2+1/3+1/4)*(1/2+1/3+1/4)+1/5*(1+1/2+1/3+1/4)-(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4)
=1/5*(1+1/2+1/3+1/4)-1/5*(1/2+1/3+1/4)
=1/5
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(1+1/2+1/3+1/4)×(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4+1/5)×(1/2+1/3+1/4)
=(1+1/2+1/3+1/4)×(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)×(1/2+1/3+1/4)-1/5×(1/2+1/3+1/4)
=(1+1/2+1/3+1/4)×[(1/2+1/3+1/4+1/5)-(1/2+1/3+1/4)]-1/5×(1/2+1/3+1/4)
=(1+1/2+1/3+1/4)×[1/2+1/3+1/4+1/5-1/2-1/3-1/4]-1/5×(1/2+1/3+1/4)
=(1+1/2+1/3+1/4)×1/5-1/5×(1/2+1/3+1/4)
=1/5×[(1+1/2+1/3+1/4)-(1/2+1/3+1/4)]
=1/5×(1+1/2+1/3+1/4-1/2-1/3-1/4)
=1/5×1
=1/5
=(1+1/2+1/3+1/4)×(1/2+1/3+1/4+1/5)-(1+1/2+1/3+1/4)×(1/2+1/3+1/4)-1/5×(1/2+1/3+1/4)
=(1+1/2+1/3+1/4)×[(1/2+1/3+1/4+1/5)-(1/2+1/3+1/4)]-1/5×(1/2+1/3+1/4)
=(1+1/2+1/3+1/4)×[1/2+1/3+1/4+1/5-1/2-1/3-1/4]-1/5×(1/2+1/3+1/4)
=(1+1/2+1/3+1/4)×1/5-1/5×(1/2+1/3+1/4)
=1/5×[(1+1/2+1/3+1/4)-(1/2+1/3+1/4)]
=1/5×(1+1/2+1/3+1/4-1/2-1/3-1/4)
=1/5×1
=1/5
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