\(\left(x-1\right)\cdot7=\left(x+5\right)\cdot6\Leftrightarrow7x-7=6x+30\Leftrightarrow x=37\)

\(7\left(x-1\right)=6\left(x+5\right)\\ \Leftrightarrow7x-7=6x+30\\ \Leftrightarrow x=37\)

mấy bạn cho mình hỏi là vì sao lại ra được 37 được không  mình hơi yếu toán nên không hiểu mấy :(

\(\begin{array}{l}a)\dfrac{x}{6} = \dfrac{{ - 3}}{4}\\x = \dfrac{{( - 3).6}}{4}\\x = \dfrac{{ - 9}}{2}\end{array}\)

Vậy \(x = \dfrac{{ - 9}}{2}\)

\(\begin{array}{l}b)\dfrac{5}{x} = \dfrac{{15}}{{ - 20}}\\x = \dfrac{{5.( - 20)}}{{15}}\\x = \dfrac{{ - 20}}{3}\end{array}\)

Vậy \(x = \dfrac{{ - 20}}{3}\)

\(a,\dfrac{x-1}{x+5}=\dfrac{6}{7}\\ \Leftrightarrow\left(x-1\right).7=6\left(x+5\right)\\ \Rightarrow7x-7=6x+30\\ \Rightarrow7x-6x=7+30\\ \Rightarrow x=37\)

Vậy \(x=37\)

\(b,\dfrac{x^2}{6}=\dfrac{24}{25}\\ \Leftrightarrow x^2.25=24.6\\ \Rightarrow x^2.5^2=144\\ \Rightarrow\left(5x\right)^2=144\\ \Rightarrow\left(5x\right)^2=\left(\pm12\right)^2\\ \Rightarrow\left\{{}\begin{matrix}5x=12\\5x=-12\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}x=\dfrac{12}{5}\\x=-\dfrac{12}{5}\end{matrix}\right.\)

Vậy \(x=\pm\dfrac{12}{5}\)

a) \(\dfrac{x}{27}=\dfrac{-2}{3,6}\)

=> x. 3,6 = 27. (-2)

=> x.3,6 = -54

x = (-54) : 3,6

x = -15

b) -0,52 : x = -9,36 : 16,38

- 0,52 : x = \(\dfrac{-4}{7}\)

x = \(\dfrac{-4}{7}\) . ( -0,52)

x = \(\dfrac{52}{175}\)

Lời giải:

a)

b)

-0,52 : x = -9,36: 16,38 => -0,52 . 16,38 = x. (-9,36) => x = -8,5176: ( -9,36) => x = 0,91

c)

a)\(\dfrac{x}{27}=\dfrac{-2}{3,6}\)

=>x.3,6=27.(-2)

=>x . 3,6=-54

=>x=-54:3.6

=>x=-54:\(\dfrac{18}{5}\)

=>x=-54.\(\dfrac{5}{18}\)

=>x=-15

b)-0,52:x=-9,36:16,38

-\(\dfrac{13}{25}:x=-\dfrac{234}{25}:\dfrac{819}{50}\)

\(-\dfrac{13}{25}:x=-\dfrac{4}{7}\)

\(x=-\dfrac{4}{7}:\left(-\dfrac{13}{25}\right)\)

x=\(\dfrac{52}{175}\)

c)\(\dfrac{4\dfrac{1}{4}}{2\dfrac{7}{8}}=\dfrac{x}{1,61}\)

\(\dfrac{\dfrac{17}{4}}{\dfrac{23}{8}}=\dfrac{x}{1,61}\)

\(\dfrac{17}{4}:\dfrac{23}{8}=\dfrac{x}{1,61}\)

\(\dfrac{17}{4}.\dfrac{8}{23}=\dfrac{x}{1,61}\)

\(\dfrac{34}{23}=\dfrac{x}{1,61}\)

=>34.1,61=x.23

rồi bạn tự tính tự làm nốt nhé

Cái này chỉ cần làm quy tắc nhân chéo là ra rồi nhé :)

a) \(x=\dfrac{-2,6.42}{-12}\)=9,1

b) x = \(\dfrac{2,5.12}{1.5}\) = 20

c) Nhân chéo: 7.(x-1) = 6.(x+5)

<=> 7x - 7 = 6x +30

<=> 7x - 6x = 7 + 30 (chuyển vế)

-> x = 37

d) Nhân chéo: 25x² = 24.6 = 144

x² = \(\dfrac{144}{25}\)=5,76

-> x = \(\sqrt{5,76}\) = 2,4

e) Nhân chéo: (x-2)² = 4.9 = 36

Ta dễ thấy (x-2)² = 6²

-> x-2 = 6 -> x = 6+2 = 8

TICK NHÉ :)

Ta có : \(\dfrac{5}{3} = \dfrac{x}{9} \Rightarrow 5.9 = 3x \Leftrightarrow 45 = 3x \Rightarrow x = 45:3\)

\( \Rightarrow \) x = 15

Vậy x = 15

a) Ta có:\(\dfrac{x-3}{x+5}=\dfrac{5}{7}\)

\(\Rightarrow7\left(x-3\right)=5\left(x+5\right)\)

\(\Rightarrow7x-21=5x+25\)

\(\Rightarrow7x-5x=21+25\)

\(\Rightarrow2x=46\)

\(\Rightarrow x=46:2=23\)

\(a,\dfrac{x-3}{x+5}=\dfrac{5}{7}\\ \Leftrightarrow7x-21=5x+25\\ \Leftrightarrow2x=46\\ \Leftrightarrow x=23\)

Vậy......

\(b,\dfrac{x+4}{20}=\dfrac{5}{x+4}\\ \Leftrightarrow\left(x+4\right)^2=100\\ \Leftrightarrow x+4=\pm10\\ \Leftrightarrow x\in\left\{-14;6\right\}\)

Vậy.........

b) Ta có: \(\dfrac{x+4}{20}=\dfrac{5}{x+4}\)

\(\Rightarrow\left(x+4\right)^2=20.5=100=10^2\)

\(\Rightarrow\left[{}\begin{matrix}x+4=10\\x+4=-10\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=10-4\\x=-10-4\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=6\\x=-14\end{matrix}\right.\)