1/12+1/36+1/54+1/72+1/90+1/110=(1/36+1/54)+(1/72+1/90+1/110)+1/12
=(1/4.9+1/9.6)+(1/8.9+1/9.10+1/10.11)+1/12
=1/5.1/3.(5/4.9+3/9.6)+(1/8-1/9+1/9-1/10+1/10_1/11) +1/12
=1/5.1/3.(1/4-1/9+1/9-1/6)+(1/8-1/11)+1/12
=1/5.1/3.(1/4-1/6)+3/88+1/12
=1/15.1/12+7/66
ket qua cuoi cung ban tu tinh nhe
nho thank nhe/

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