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a=-3/4; b=4/7 =>ab=-3/7
\(a=\dfrac{5}{9};b=-\dfrac{18}{15}=-\dfrac{6}{5}\Leftrightarrow ab=-\dfrac{2}{3}\)
\(a=-\dfrac{7}{25};b=\dfrac{50}{21}\Leftrightarrow ab=-\dfrac{2}{3}\)
\(ab=1;b=-\dfrac{3}{7}\Leftrightarrow a=-\dfrac{7}{3}\)
\(a=\dfrac{4}{7};b=-\dfrac{3}{4}\Leftrightarrow ab=-\dfrac{3}{7}\)
\(a=\dfrac{-4}{19};ab=-\dfrac{4}{19}\Leftrightarrow b=1\)
\(a=-\dfrac{18}{15}=-\dfrac{6}{5};c=\dfrac{5}{9}\Leftrightarrow ab=-\dfrac{2}{3}\)
\(ab=0;b=\dfrac{6}{13}\Leftrightarrow a=0\)

a: 17/200>17/314
b: 11/54=22/108<22/37
c: 141/893=3/19
159/901=3/17
mà 3/19<3/17
nên 141/893<159/901

a | \(\dfrac{-2}{3}\) | \(\dfrac{4}{15}\) | \(\dfrac{9}{4}\) | \(\dfrac{5}{9}\) | \(\dfrac{5}{4}\) | \(\dfrac{4}{16}\) | 0 | \(\dfrac{12}{18}\) | \(\dfrac{-4}{10}\) | 0 |
b | \(\dfrac{4}{5}\) | \(\dfrac{5}{8}\) | \(\dfrac{-2}{3}\) | \(\dfrac{5}{14}\) | \(\dfrac{-2}{4}\) | 1 | \(\dfrac{-5}{12}\) | 0 | \(\dfrac{-17}{42}\) | |
a.b | \(\dfrac{-8}{5}\) | \(\dfrac{1}{6}\) | \(\dfrac{-3}{2}\) | \(\dfrac{25}{126}\) | \(\dfrac{-5}{8}\) | \(\dfrac{4}{16}\) | 0 | \(\dfrac{12}{18}\) | 0 | 0 |

Câu 1:
a) \(\dfrac{-15}{17}\) và \(\dfrac{-19}{21}\)
Ta có: \(\dfrac{-15}{17}=-1+\dfrac{2}{17}\); \(\dfrac{-19}{21}=-1+\dfrac{2}{21}\)
Vì \(\dfrac{2}{17}>\dfrac{2}{21}\)
Do đó: \(\dfrac{-15}{17}>\dfrac{19}{-23}\)
b) \(\dfrac{-13}{19}\) và \(\dfrac{19}{-23}\)
Ta có: \(\dfrac{19}{23}>\dfrac{19}{25}\); \(\dfrac{13}{19}=1-\dfrac{6}{19}\); \(\dfrac{19}{25}=1-\dfrac{6}{25}\)
mà \(\dfrac{6}{19}>\dfrac{6}{25}\) \(\Rightarrow\dfrac{13}{19}< \dfrac{19}{25}< \dfrac{19}{23}\)
Vì \(\dfrac{13}{19}< \dfrac{19}{23}\Rightarrow\dfrac{-13}{19}>\dfrac{19}{-23}\)
c) \(\dfrac{-24}{35}\) và \(\dfrac{-19}{30}\)
Ta có: \(\dfrac{-24}{35}=-1+\dfrac{19}{35}\);\(\dfrac{-19}{30}=-1+\dfrac{11}{30}\)
Vì \(\dfrac{11}{35}< \dfrac{11}{30}\)
Do đó: \(\dfrac{-24}{35}< \dfrac{-19}{30}\)
d) \(\dfrac{-1941}{1931}\) và \(\dfrac{-2011}{2001}\); \(\dfrac{-2011}{2001}=-1+\dfrac{10}{2001}\)
Vì \(\dfrac{10}{1931}< \dfrac{10}{1001}\)
Do đó: \(\dfrac{-1941}{1931}< \dfrac{-2011}{2001}\)
Ta có: \(\dfrac{-1941}{1931}=-1+\dfrac{10}{1931}\)
Sorry câu d mình viết ngược:
Làm lại:
d) \(\dfrac{-1941}{1931}\) và \(\dfrac{-2011}{2001}\)
Ta có: \(\dfrac{-1941}{1931}=-1+\dfrac{10}{1931};\)
\(\dfrac{-2011}{2001}=-1+\dfrac{10}{2001}\)
Vì \(\dfrac{10}{1931}< \dfrac{10}{1001}\)
Do đó: \(\dfrac{-1941}{1931}< \dfrac{-2011}{2001}\)

a: \(\dfrac{-5}{6}=\dfrac{-20}{24};\dfrac{7}{8}=\dfrac{21}{24};\dfrac{7}{24}=\dfrac{7}{24};\dfrac{-3}{4}=-\dfrac{18}{24};\dfrac{2}{3}=\dfrac{16}{24}\)
Do đó: \(\dfrac{-5}{6}< -\dfrac{3}{4}< \dfrac{7}{24}< \dfrac{2}{3}< \dfrac{7}{8}\)
\(\dfrac{7}{8}=\dfrac{119}{136};\dfrac{16}{17}=\dfrac{128}{136}\)
mà 119<128
nên 7/8<16/17
DO đó: -5/6<-3/4<7/24<2/3<7/8<16/17
b: \(\dfrac{-5}{8}=\dfrac{-95}{8\cdot19};\dfrac{-16}{19}=\dfrac{-128}{19\cdot8}\)
Do đó: -5/8>-16/19
\(\dfrac{7}{10}=0.7;\dfrac{20}{23}\simeq0.87;\dfrac{214}{315}\simeq0.68;\dfrac{205}{107}>1\)
Do đó: \(\dfrac{205}{107}>\dfrac{20}{23}>\dfrac{7}{10}>\dfrac{214}{315}>-\dfrac{5}{8}>-\dfrac{16}{19}\)