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a: \(\dfrac{20}{30}=\dfrac{2}{3}\)
\(\dfrac{30}{45}=\dfrac{2}{3}\)
Do đó: \(\dfrac{20}{30}=\dfrac{30}{45}\)
b: \(\dfrac{-25}{35}=\dfrac{-5}{7}\)
\(\dfrac{-55}{77}=\dfrac{-5}{7}\)
Do đó: \(-\dfrac{25}{35}=-\dfrac{55}{77}\)
a,20/30=2/3
30/45=2/3
->20/30=30/45
b -25/35=-5/7
-55/77=-5/7
-> -25/35=-55/77
a: 20/30=2/3
30/45=2/3
=>20/30=30/45
b: -25/35=-5/7
-55/77=-5/7
=>-25/35=-55/77
36 84 = 36 : 12 84 : 12 = 3 7 42 98 = 42 : 14 98 : 14 = 3 7 D o đ ó 36 84 = 42 98
a) − 18 − 30 = − 18 : 6 − 30 : 6 = 3 5 ; − 39 65 = − 39 : 13 65 : 13 = 3 5
Vậy − 18 − 30 = − 39 65
b) 23 99 = 23.101 99.101 = 2323 9999
. b.
. c. 
.
Bài 5:
\(\dfrac{3}{4}=\dfrac{x}{20}=\dfrac{21}{y}\)
=>\(\left\{{}\begin{matrix}\dfrac{x}{20}=\dfrac{3}{4}\\\dfrac{21}{y}=\dfrac{3}{4}\end{matrix}\right.\)
=>\(\left\{{}\begin{matrix}x=20\cdot\dfrac{3}{4}=15\\y=21\cdot\dfrac{4}{3}=7\cdot4=28\end{matrix}\right.\)
Bài 4:
a: \(\dfrac{3}{5}=\dfrac{3\cdot9}{5\cdot9}=\dfrac{27}{45}\)
b: Đề sai rồi bạn
Bài 3:
a: \(21\cdot21=441\)
\(49\cdot9=441\)
=>\(21\cdot21=49\cdot9\)
=>\(\dfrac{21}{9}=\dfrac{49}{21}\)
b: \(\dfrac{-24}{34}=\dfrac{-24:2}{34:2}=\dfrac{-12}{17}\)
\(\dfrac{-60}{85}=\dfrac{-60:5}{85:5}=\dfrac{-12}{17}\)
Do đó: \(\dfrac{-24}{34}=\dfrac{-60}{85}\)
Bài 2:
\(15cm=\dfrac{3}{20}m\)
\(40mm=\left(\dfrac{40}{1000}\right)m=\dfrac{1}{25}m\)
Bài 1:
a: \(\left(-17\right):8=\dfrac{-17}{8}\)
b: \(\left(-8\right):\left(-9\right)=\dfrac{-8}{-9}\)
\(\dfrac{20}{30}=\dfrac{20:10}{30:10}=\dfrac{2}{3}\)
\(\dfrac{30}{45}=\dfrac{30:15}{45:15}=\dfrac{2}{3}\)
Ta thấy\(\dfrac{2}{3}=\dfrac{2}{3}\Rightarrow\dfrac{20}{30}=\dfrac{30}{45}\)