Quy đồng mẫu số sau: 20/45 ; 14/35 ; 32/44
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Không quy đồng mẫu số hãy so sánh các phân số sau :
a.19/20 và 20/21
b.17/21 và 23/27 3
c.1/29 và 45/43
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a. 19/ 20= 1- 1/20
20/ 21= 1- 1/21
mà 1/20> 1/21 => 19/ 20< 20/ 21
b. 17/ 21= 1- 4/21
23/ 27= 1- 4/27
mà 4/21< 4/27 => 17/21< 23/27
c. 31/29= 1+ 2/29
45/43= 1+ 2/43
mà 2/29> 2/43 => 31/29> 45/43
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a)
− 25 − 45 = 5 9 = 10 18 − 24 48 = − 1 2 = − 9 18
b)
1 5 = 7 35 − 2 = − 70 35 3 7 = 15 35
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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
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\(\frac{1}{3};\frac{2}{15};\frac{4}{45}\)
Ta có : Mẫu số chung là 45 vì \(45\) \(⋮3;15\)
\(\frac{1}{3}=\frac{1.15}{3.15}=\frac{15}{45}\)
\(\frac{2}{15}=\frac{2.3}{15.3}=\frac{6}{45}\)
Còn \(\frac{4}{45}\)ta giữ nguyên.
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MSC : 360
`5/8 = (5xx45)/(8xx45)=225/360`
`7/20=(7xx18)/(20xx18)=126/360`
`-4/9=(-4xx40)/(9xx40)=-160/360`
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13/30=138/180
38/45=152/180
7/12=156/180
17/20=153/180
13/18=130/180
Thứ tự tăng dần là : 130/180;138/180;152/180;153/180;156/180
=>13/18;13/30;38/45;17/20;7/12
Chúc bạn học tốt
Ta có:
\(\dfrac{20}{45}=\dfrac{5}{9}\)
\(\dfrac{14}{35}=\dfrac{2}{5}\)
\(\dfrac{32}{44}=\dfrac{8}{11}\)
Mẫu số chung là: 495
\(\dfrac{5}{9}=\dfrac{5\cdot55}{9\cdot55}=\dfrac{275}{495}\)
\(\dfrac{2}{5}=\dfrac{2\cdot99}{5\cdot99}=\dfrac{198}{495}\)
\(\dfrac{8}{11}=\dfrac{8\cdot45}{11\cdot45}=\dfrac{360}{495}\)
\(\dfrac{20}{45}\) = \(\dfrac{4}{9}\) = \(\dfrac{4.5.11}{9.5.11}\) = \(\dfrac{220}{495}\)
\(\dfrac{14}{35}\) = \(\dfrac{2}{5}\) = \(\dfrac{2.9.11}{9.5.11}\) = \(\dfrac{198}{495}\)
\(\dfrac{32}{44}\) = \(\dfrac{8}{11}\) = \(\dfrac{8.9.5}{9.5.11}\)= \(\dfrac{360}{495}\)