HOC24
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Môn học
Chủ đề / Chương
Bài học
`1/3-5/6+3/2`
`=2/6-5/6+9/6`
`=-3/6+9/6`
`=6/6`
`=1`
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`2/13-(15/13+4-0,5)`
`=2/13-1513-4+0,5`
`=(2/13-15/13)-4,5`
`=-13/13-4,5`
`=-1-4,5`
`=-5,5`
`-(1/9+7/5-3/11)+(-2/5+17/9-8/11)`
`=-1/9-7/5+3/11+(-2)/5+17/9-8/11`
`=(-1/9+17/9)+(-7/5+(-2)/5)+(3/11-8/11)`
`=16/9-9/5-5/11`
`=-236/495`
`5,75-3,25+5 5/6`
`=5/2+35/6`
`=15/6+35/6`
`=50/6`
`=25/3`
`S=1/(2^2)-1/(2^4)+1/(2^6)-...+1/(2^(4n-2)2^(4n))+...+1/(2^2018)-1/(2^2020)`
`S=1/(2^2)-1/(2^4)+1/(2^6)-...+1/(2^(4n-2))-1/(2^(4n))+...+1/(2^2018)-1/(2^2020)`
`2^2S=2^2(1/(2^2)-1/(2^4)+1/(2^6)-...+1/(2^(4n-2))-1/(2^(4n))+...+1/(2^2018)-1/(2^2020))`
`4S=1-1/(2^2)+1/(2^4)-1/(2^6)+...-1/(2^(4n-2))+1/(2^(4n))-...-1/(2^2018)`
`4S+S=(1-1/(2^2)+1/(2^4)-1/(2^6)+...-1/(2^(4n-2))+1/(2^(4n))-...-1/(2^2018))+(1/(2^2)-1/(2^4)+1/(2^6)-...+1/(2^(4n-2))-1/(2^(4n))+...+1/(2^2018)-1/(2^2020))`
`5S=1-1/(2^2020)`
`=>S=(1-1/(2^2020)):5`
`=>S=1:5-1/(2^2020):5`
`=>S=1/5-1/(2^2020) .1/5`
`=>S=1/5-1/(2^2020. 5)<1/5`
`=>S<0,2(đpcm)`
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uaa=)) v là t bị lừaaa