Bài 1: Lập tất cả các tỉ lệ thức có được từ các số sau:
a) 3; 9; 27; 81
b) 1; 5; 25; 125; 625
c) -5; -1,2; 15; 3,6
d) 4; 8; 8; 18
Bài 2: Tìm x trong tỉ lệ thức sau:
a) 2,5 : 7,5 = x : \(\frac{3}{5}\) b) \(2\frac{2}{3}\) : x = \(1\frac{7}{9}\) : 0,2
c) \(\frac{x}{5}\) = \(\frac{4}{10}\) d) \(\frac{18}{7}\) = \(\frac{x}{21}\)
e) \(\frac{x}{6}\) = \(\frac{24}{x}\)
Bài 1 khó hiểu quá
Bài 2:
a)2,5:7,5=x:\(\frac{3}{5}\)
x:\(\frac{3}{5}\)=\(\frac{1}{3}\)
x=\(\frac{1}{3}.\frac{3}{5}\)
\(x=\frac{1}{5}\)
Vậy \(x=\frac{1}{5}\)
b)\(2\frac{2}{3}:x=1\frac{7}{9}:0,2\)
\(2\frac{2}{3}:x=\frac{80}{9}\)
\(x=2\frac{2}{3}:\frac{80}{9}\)
\(x=\frac{3}{10}\)
Vậy \(x=\frac{3}{10}\)
c)\(\frac{x}{5}=\frac{4}{10}\)
\(\Rightarrow x.10=4.5\)
\(\Rightarrow x.10=20\)
\(\Rightarrow x=2\)
Vậy x=2
d)\(\frac{18}{7}=\frac{x}{21}\)
\(\Rightarrow x.7=18.21\)
\(\Rightarrow x.7=378\)
\(\Rightarrow x=54\)
Vậy x=54
e)\(\frac{x}{6}=\frac{24}{x}\)
\(\Rightarrow x.x=24.6\)
\(\Rightarrow x^2=144=12^2=\left(-12\right)^2\)
Do đó:x=12;-12
Vậy x=-12;12
Bài 2,
a, 2,5 : 7,5 = x : \(\frac{3}{5}\)
\(\frac{1}{3}\) = x : \(\frac{3}{5}\)
x = \(\frac{1}{3}\) . \(\frac{3}{5}\)
x = \(\frac{1}{5}\)
b , \(2\frac{2}{3}\) : x = \(1\frac{7}{9}\) : 0,2
\(\frac{8}{3}\) : x = \(\frac{16}{9}\) : 0.2
\(\frac{8}{3}\) : x = \(\frac{80}{9}\)
x = \(\frac{8}{3}\) :\(\frac{80}{9}\)
x = 0,3
c, \(\frac{x}{5}\) = \(\frac{4}{10}\)
\(\Rightarrow\) 10x = 4.5 = 20
x = 20 : 10
x = 2
d,\(\frac{18}{7}\) = \(\frac{x}{21}\)
\(\Rightarrow\) 18.21 = 7x
378 = 7.x
x = 378 : 7
x = 54
e,\(\frac{x}{6}\) = \(\frac{24}{x}\)
\(\Rightarrow\) x2 = 6 . 24
x2 = 144
\(\Rightarrow\) x = \(\pm\) 12
cảm ơn hai bạn Jenny Trương và Nobi Nobita nhé
Bài 2: Tìm x trong tỉ lệ thức:
a) \(2,5:7,5=x:\dfrac{3}{5}\)
\(\Rightarrow2,5.\dfrac{3}{5}=7,5x\)
\(\Rightarrow\dfrac{3}{2}=7,5x\)
\(\Rightarrow x=\dfrac{3}{2}:7,5\)
\(\Rightarrow x=\dfrac{1}{5}\)
Vậy \(x=\dfrac{1}{5}\)
b) \(2\dfrac{2}{3}:x=1\dfrac{7}{9}:0,2\)
\(\Rightarrow2\dfrac{2}{3}.0,2=1\dfrac{7}{9}.x\)
\(\Rightarrow\dfrac{8}{15}=\dfrac{16}{9}x\)
\(\Rightarrow x=\dfrac{8}{15}:\dfrac{16}{9}\)
\(\Rightarrow x=\dfrac{3}{10}=0,3\)
Vậy \(x=0,3\)
c) \(\dfrac{x}{5}=\dfrac{4}{10}\)
\(\Rightarrow10.x=4.5\)
\(\Rightarrow10x=20\)
\(\Rightarrow x=\dfrac{20}{10}\)
\(\Rightarrow x=2\)
Vậy \(x=2\)
d) \(\dfrac{18}{7}=\dfrac{x}{21}\)
\(\Rightarrow18.21=7.x\)
\(\Rightarrow378=7x\)
\(\Rightarrow x=\dfrac{378}{7}\)
\(\Rightarrow x=54\)
Vậy \(x=54\)
e) \(\dfrac{x}{6}=\dfrac{24}{x}\)
\(\Rightarrow x.x=6.24\)
\(\Rightarrow x^2=144\)
\(\Rightarrow x^2=12^2\)
\(\Rightarrow x=12\)
Vậy \(x=12\)
