
简算1×6分之1+6×11分之1+11×16分之1+....+101×106分之1
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用裂项法:
原式
= 1/(1×6)+1/(6×11)+1/(11×16)+……+1/(101×106)
= (1/5)×(1-1/6)+(1/5)×(1/6-1/11)+(1/5)×(1/11-1/16)+……+(1/5)×(1/101-1/106)
= (1/5)×[(1-1/6)+(1/6-1/11)+(1/11-1/16)+……+(1/101-1/106)]
= (1/5)×(1-1/106)
= 21/106
原式
= 1/(1×6)+1/(6×11)+1/(11×16)+……+1/(101×106)
= (1/5)×(1-1/6)+(1/5)×(1/6-1/11)+(1/5)×(1/11-1/16)+……+(1/5)×(1/101-1/106)
= (1/5)×[(1-1/6)+(1/6-1/11)+(1/11-1/16)+……+(1/101-1/106)]
= (1/5)×(1-1/106)
= 21/106
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