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\(=2-\left(\dfrac{5}{3}-\dfrac{7}{6}+\dfrac{9}{10}-...-\dfrac{19}{45}\right)\)
\(=2-2\left(\dfrac{5}{6}-\dfrac{7}{12}+\dfrac{9}{20}-...-\dfrac{19}{90}\right)\)
\(=2-2\left(\dfrac{1}{2}+\dfrac{1}{3}-\dfrac{1}{3}-\dfrac{1}{4}+\dfrac{1}{4}+\dfrac{1}{5}-...-\dfrac{1}{9}-\dfrac{1}{10}\right)\)
\(=2-2\cdot\dfrac{4}{10}=2-\dfrac{8}{10}=2-\dfrac{4}{5}=\dfrac{6}{5}\)
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a,M=3/8+3/7+3/15=>M=843/840>840/840=>M=843/840>1(dpcm)
b,P=41/90+31/72+21/40+11/45+(-1)/36=293/180>180/180(dpcm)
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Bài giải
Ta có : \(\frac{21}{11}+\frac{19}{30}+\frac{11}{36}=\frac{3780}{1980}+\frac{1254}{1980}+\frac{605}{1980}=\frac{5639}{1980}< \frac{5940}{1980}=3\left(đpcm\right)\)
ờm,... Xin lỗi bạn nha ,cách của mình có thô sơ tí ,hihihihi ,xin lỗi bạn nhiều !!!
cho A=1,01+1,02+1,03+...+9,98+9,99+10
B=2-5/3+7/6-9/10+11/15-13/21+15/28-17/36+19/45
tinh 2A+455/3(B)
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Ta có: 21/11 + 19/36 + 11/36 = 21/11 + ( 19/36 + 11/36 ) = 21/11 + 30/36 = 21/11 + 5/6 = 126/66 + 55/66 = 181/66 = \(2\frac{49}{66}\)
Mà \(2\frac{49}{66}< 3\Rightarrow\frac{21}{11}+\frac{19}{36}+\frac{11}{36}< 3\)
Chắc vậy! k cho mình nha!
Ta có: \(\frac{21}{11}-1+\frac{19}{36}-1+\frac{11}{36}-1=\frac{10}{11}-\frac{7}{6}=-\frac{17}{66}< 0.\)
\(\Rightarrow\frac{21}{11}+\frac{19}{36}+\frac{11}{36}< 3lđ.\)
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