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1 / 6 + 1 / 10 + 1 / 15 + 1 / 21 + 1 / 28 + 1 / 36 + 1 / 45
= 2 / 12 + 2 / 10 + 2 / 30 + 2 / 42 + 2 / 56 + 2 / 72 + 2 / 90
= 2 ( 1 / 3 . 4 + 1 / 4 . 5 + 1 / 5 . 6 + 1 / 6 . 7 + 1 / 7 . 8 + 1 / 8 . 9 + 1 / 9 . 10 )
= 2 .( 1 / 3 - 1 / 4 + 1 / 4 - 1/ 5 + 1 / 5 - 1 / 6 + 1 / 6 - 1 / 7 + 1 / 7 - 1 / 8 + 1 / 8 - 1 / 9 +1 / 9 - 1 / 10)
=2 ( 1 / 3 - 1 / 10 )
= 2. 7 / 30
= 7 / 15
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1: 0,35*12,4=0,35*2,4+0,35*10=3,5+0,84=4,34
2: =0,1-2,34=-2,24
3: =5-2,9=2,1
4: \(=2,5\left(10,124-0,124\right)=10\cdot2,5=25\)
5: =-3/7+1/13
=-39/91+7/91
=-32/91
6: =-1/3+1/3=0
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de vai dai ra ma ko bik lm a dap an la?????????tu hieu cho minh nhe hihi bye
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A= 20/21.27/28.35/36...1325/1326
= 40/42.54/56.70/72...2650/2652
=5.8.6.9.7.10.../6.7.7.8.8.9..
còn đâu tự làm
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