Quy đồng mẫu số các phân số sau: 3/7 ; 4/9 ;và 8/21
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\(\frac{3}{5}=\frac{3\times8}{5\times8}=\frac{24}{40}\)
\(\frac{3}{8}=\frac{3\times5}{8\times5}=\frac{15}{40}\)
\(\frac{3}{10}=\frac{3\times4}{10\times4}=\frac{12}{40}\)
\(\frac{3}{2}=\frac{3\times20}{2\times20}=\frac{60}{40}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
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, \(\dfrac{{20}}{{28}} + \dfrac{{ - 21}}{{28}} = \dfrac{{20 + \left( { - 21} \right)}}{{28}} = \dfrac{-1}{{28}}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
bài3
1. \(\frac{4}{3}\)= \(\frac{4x4}{3x4}\)=\(\frac{20}{12}\)
\(\frac{3}{4}\)=\(\frac{3x3}{4x3}\)=\(\frac{9}{12}\)
2.\(\frac{5}{4}\)=\(\frac{5x6}{4x6}\)=\(\frac{30}{24}\)
\(\frac{5}{6}\)=\(\frac{5x4}{6x4}\)=\(\frac{20}{24}\)
3.\(\frac{3}{8}\)=\(\frac{3x6}{8x6}\)=\(\frac{18}{48}\)
\(\frac{1}{6}\)=\(\frac{1x6}{6x8}\)=\(\frac{6}{48}\)
4.\(\frac{2}{5}\)=\(\frac{2x7}{5x7}\)=\(\frac{14}{35}\)
\(\frac{4}{7}\)=\(\frac{4x5}{7x5}\)=\(\frac{20}{35}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{3}{5}=\frac{24}{40};\frac{3}{8}=\frac{15}{40};\frac{3}{10}=\frac{12}{40};\frac{3}{2}=\frac{60}{40}\)
\(\frac{3}{5}=\frac{3\times8}{5\times8}=\frac{24}{40}\)
\(\frac{3}{8}=\frac{3\times5}{8\times5}=\frac{15}{40}\)
\(\frac{3}{10}=\frac{3\times4}{10\times4}=\frac{12}{40}\)
\(\frac{3}{2}=\frac{3\times20}{2\times20}=\frac{60}{40}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 3 :
a: \(MSC:12\\ \dfrac{4}{3}=\dfrac{4\times4}{3\times4}=\dfrac{16}{12};\dfrac{3}{4}=\dfrac{3\times3}{3\times4}=\dfrac{9}{12}\)
b: \(MSC:12\\ \dfrac{5}{4}=\dfrac{5\times3}{4\times3}=\dfrac{15}{12};\dfrac{5}{6}=\dfrac{5\times2}{6\times2}=\dfrac{10}{12}\)
c:\(MSC:24\\ \dfrac{3}{8}=\dfrac{3\times3}{8\times3}=\dfrac{9}{24};\dfrac{1}{6}=\dfrac{1\times2}{6\times2}=\dfrac{2}{12}\)
d: \(MSC:35\\ \dfrac{2}{5}=\dfrac{2\times7}{5\times7}=\dfrac{14}{35};\dfrac{4}{7}=\dfrac{4\times5}{7\times5}=\dfrac{20}{35}\)
Bài 3:
a: 4/3=16/12
3/4=9/12
b: 5/4=30/24
5/6=20/24
c: 3/8=18/48
1/6=8/48
d: 2/5=14/35
4/7=20/35
Bài 4:
a: 7/12=28/48
5/48=5/48
b: 4/100=4/100
8/25=32/100
![](https://rs.olm.vn/images/avt/0.png?1311)
Quy đồng p/số : \(\frac{-3}{8};\frac{7}{-12}\)
\(\frac{7}{-12}=\frac{-7}{12}\)
\(BCNN\left(8;12\right)=2^3.3=24\)
\(24:8=3\)
\(24:12=2\)
\(\frac{-3}{8}=\frac{\left(-3\right).3}{8.3}=\frac{-9}{24}\)
\(\frac{-7}{12}=\frac{\left(-7\right).2}{12.2}=\frac{-14}{24}\)
tk mk nha
hihi yêu mọi người nhiều ạ !!!!!!!
-3/8 và 7/-12
-3/8=-9/24; 7/-12=-7/12=-14/21
Vậy ...
CHÚC BẠN HỌC TỐT NHA ><
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ok cảm ơn