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a: -5/5=-1=-7/7
8/7=8/7
b: -3/15=-1/5=-6/30
5/6=25/30
c: -34/136=-1/4=-9/36
-12/108=-1/9=-4/36
26/-156=-1/6=-6/36
a: 3/8=36/96
5/12=40/96
b: -2/9=-24/108
-5/12=-45/108
c: -3/16=-63/336
-5/24=-70/336
-21/56=-126/336
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: \(-\dfrac{2}{5}< \dfrac{1}{3}\)
Ta có: \(\dfrac{5}{7} = \dfrac{{5.4}}{{7.4}} = \dfrac{{20}}{{28}}\) và \(\dfrac{{ - 3}}{4} = \dfrac{{ - 3.7}}{{4.7}} = \dfrac{{ - 21}}{{28}}\)
Như vậy, \(\dfrac{{20}}{{28}} + \dfrac{{ - 21}}{{28}} = \dfrac{{20 + \left( { - 21} \right)}}{{28}} = \dfrac{-1}{{28}}\)
\(BCNN\left( {4,9,3} \right) = 36\)
Thừa số phụ: \(36:4 = 9;36:9 = 4;36:3 = 12\)
Ta có :
\(\begin{array}{l}\dfrac{{ - 3}}{4} = \dfrac{{ - 3.9}}{{4.9}} = \dfrac{{ - 27}}{{36}}\\\dfrac{5}{9} = \dfrac{{5.4}}{{9.4}} = \dfrac{{20}}{{36}}\\\dfrac{2}{3} = \dfrac{{2.12}}{{3.12}} = \dfrac{{24}}{{36}}\end{array}\)
\(\dfrac{-3}{4}=\dfrac{-3.9}{4.9}=\dfrac{-27}{36}\)
\(\dfrac{5}{9}=\dfrac{5.4}{9.4}=\dfrac{20}{36}\)
\(\dfrac{2}{3}=\dfrac{2.12}{3.12}=\dfrac{24}{36}\)
a) Ta có BCNN(3,7)=21
Thừa số phụ: 21:3=7 và 21:7=3
\(\dfrac{2}{3} = \dfrac{{2.7}}{{3.7}} = \dfrac{{14}}{{21}}\) và \(\dfrac{{ - 6}}{7} = \dfrac{{ - 6.3}}{{7.3}} = \dfrac{{ - 18}}{{21}}\)
b) Ta có \(BCNN\left( {\left( {{2^2}{{.3}^2}} \right),\left( {{2^2}.3} \right)} \right) = {2^2}{.3^2}\)
Thừa số phụ \(\left( {{2^2}{{.3}^2}} \right):\left( {{2^2}.3^2} \right) = 1\) và \(\left( {{2^2}{{.3}^2}} \right):\left( {{2^2}.3} \right) = 3\)
\(\dfrac{5}{{{2^2}{{.3}^2}}}\) và \(\dfrac{{ - 7}}{{{2^2}.3}} = \dfrac{{ - 7.3}}{{{2^2}{{.3}^2}}} = \dfrac{{ - 21}}{{{2^2}{{.3}^2}}}\)