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8 tháng 1
a: \(\dfrac{-7}{6}=\dfrac{-7\cdot3}{6\cdot3}=\dfrac{-21}{18}\)
\(\dfrac{-11}{9}=\dfrac{-11\cdot2}{9\cdot2}=\dfrac{-22}{18}\)
mà -21>-22
nên \(-\dfrac{7}{6}>-\dfrac{11}{9}\)
b: \(\dfrac{5}{-7}=\dfrac{-5}{7}=\dfrac{-5\cdot5}{7\cdot5}=\dfrac{-25}{35}\)
\(\dfrac{-4}{5}=\dfrac{-4\cdot7}{5\cdot7}=\dfrac{-28}{35}\)
mà -25>-28
nên \(\dfrac{5}{-7}>\dfrac{-4}{5}\)
c: \(\dfrac{-8}{7}< -1\)
\(-1< -\dfrac{2}{5}\)
Do đó: \(-\dfrac{8}{7}< -\dfrac{2}{5}\)
d: \(-\dfrac{2}{5}< 0\)
\(0< \dfrac{1}{3}\)
Do đó: \(-\dfrac{2}{5}< \dfrac{1}{3}\)
18 tháng 2 2021
\(\dfrac{1}{1\cdot2}>\dfrac{1}{2^2}>\dfrac{1}{2\cdot3},\dfrac{1}{2\cdot3}>\dfrac{1}{3^2}>\dfrac{1}{3\cdot4},...,\dfrac{1}{8\cdot9}>\dfrac{1}{9^2}>\dfrac{1}{9\cdot10}\)
\(\Rightarrow\dfrac{1}{1\cdot2}+\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+...+\dfrac{1}{8\cdot9}>\dfrac{1}{2^2}+\dfrac{1}{3^2}+...+\dfrac{1}{9^2}>\dfrac{1}{2\cdot3}+\dfrac{1}{3\cdot4}+...+\dfrac{1}{9\cdot10}\) \(\Rightarrow1-\dfrac{1}{9}>A>\dfrac{1}{2}-\dfrac{1}{10}\) \(\Rightarrow\dfrac{8}{9}>A>\dfrac{2}{5}\)
31 tháng 5 2021
a) \(A=\dfrac{7}{8}\left(-\dfrac{5}{9}-\dfrac{4}{9}\right)+5\dfrac{7}{8}\)
\(A=\dfrac{7}{8}.\left(-1\right)+5\dfrac{7}{8}=5\dfrac{7}{8}-\dfrac{7}{8}=5\).
31 tháng 5 2021
\(B=\dfrac{1}{4}.\dfrac{8}{5}.\dfrac{25}{16}.\dfrac{-7}{4}=\dfrac{-35}{32}\)
N
18 tháng 3 2022
a,
\(x.\dfrac{1}{4}=\dfrac{1}{2}-\dfrac{4}{5}\)
\(x.\dfrac{1}{4}=\dfrac{5}{10}-\dfrac{8}{10}\)
\(x.\dfrac{1}{4}=-\dfrac{3}{10}\)
\(\Rightarrow x=-\dfrac{3}{10}:\dfrac{1}{4}\)
\(\Rightarrow x=-\dfrac{3}{10}.4\)
\(\Rightarrow x=-\dfrac{6}{5}\)
b,
\(\dfrac{2}{3}-x=\dfrac{1}{2}:\dfrac{3}{8}\)
\(\dfrac{2}{3}-x=\dfrac{1}{2}.\dfrac{8}{3}\)
\(\dfrac{2}{3}-x=\dfrac{4}{3}\)
\(x=\dfrac{2}{3}-\dfrac{4}{3}\)
\(x=-\dfrac{2}{3}\)
16 tháng 6 2021
`A=(8 2/7-4 2/7)-3 4/9`
`=8+2/7-4-2/7-3-4/9`
`=4-3-4/9`
`=1-4/9=5/9`
`B=(10 2/9-6 2/9)+2 3/5`
`=10+2/9-6-2/9+2+3/5`
`=4+2+3/5`
`=6+3/5=33/5`
Bài 2:
`a)5 1/2*3 1/4`
`=11/2*13/4`
`=143/8`
`b)6 1/3:4 2/9`
`=19/3:38/9`
`=19/3*9/38=3/2`
`c)4 3/7*2`
`=31/7*2`
`=62/7`
16 tháng 6 2021
Bài 1:
\(A=\left(8\dfrac{2}{7}-4\dfrac{2}{7}\right)-3\dfrac{4}{9}\)
\(A=\left(\dfrac{58}{7}-\dfrac{30}{7}\right)-\dfrac{31}{9}\)
\(A=4-\dfrac{31}{9}\)
\(A=\dfrac{5}{9}\)
\(B=\left(10\dfrac{2}{9}-6\dfrac{2}{9}\right)+2\dfrac{3}{5}\)
\(B=\left(\dfrac{92}{9}-\dfrac{56}{9}\right)+\dfrac{13}{5}\)
\(B=4+\dfrac{13}{5}\)
\(B=\dfrac{33}{5}\)
Ta có:
\(\dfrac{4}{8}=\dfrac{1}{2}\)
\(\dfrac{-1}{-2}=\dfrac{1}{2}\)
\(\Rightarrow\dfrac{4}{8}=\dfrac{-1}{-2}\)
\(\dfrac{4}{8}\) = \(\dfrac{1}{2}\)
\(\dfrac{-1}{-2}\) = \(\dfrac{1}{2}\)
\(\dfrac{4}{8}\) = \(\dfrac{-1}{-2}\)