a.

\(\frac{x}{4}=\frac{3}{2}\)

\(x=\frac{3}{2}\times4\)

\(x=6\)

b.

\(\frac{x}{16}=\frac{9}{x}\)

\(x\times x=16\times9\)

\(x^2=144\)

\(x^2=\left(\pm12\right)^2\)

\(x=\pm12\)

Vậy \(x=12\) hoặc \(x=-12\)

c.

\(\frac{x^2}{6}=\frac{24}{25}\)

\(x^2=\frac{24}{25}\times6\)

\(x^2=\frac{144}{25}\)

\(x^2=\left(\pm\frac{12}{5}\right)^2\)

\(x=\pm\frac{12}{5}\)

Vậy \(x=\frac{12}{5}\) hoặc \(x=-\frac{12}{5}\)

d.

\(\frac{72-9}{7}=\frac{x-40}{9}\)

\(\frac{x-40}{9}=\frac{63}{7}\)

\(x-40=\frac{63}{7}\times9\)

\(x-40=81\)

\(x=81+40\)

\(x=121\)

\(\Leftrightarrow\frac{\left(x+2\right)\left(x-2\right)}{x\left(x+2\right)}=\frac{A}{x}\)

\(\Leftrightarrow\frac{x-2}{x}=\frac{A}{x}\)

\(\Rightarrow A=x-2\)

^_gggggggg

a) x= 23

b) x=8

\(\frac{x-3}{x+5}=\frac{5}{7}\)

=> 7 ( x - 3 ) = 5 ( x + 5 )

7x - 21 = 5x + 25

7x - 5x = 25 + 21

2x = 46

x = 23

\(\frac{x-3}{x+5}=\frac{5}{7}\)

=>   \(7\left(x-3\right)=5\left(x+5\right)\)

<=>  \(7x-21=5x+25\)

<=>  \(2x=46\)

<=>  \(x=23\)

Vậy...

\(\frac{7}{x-1}=\frac{x+1}{9}\)

<=>  \(\left(x-1\right)\left(x+1\right)=63\)

<=>  \(x^2-1=63\)

<=>  \(x^2=64\)

<=>  \(x=\pm8\)

Vậy...

1.

b) \(\frac{72-x}{7}=\frac{x-40}{9}\)

\(\Rightarrow\left(72-x\right).9=\left(x-40\right).7\)

\(\Rightarrow648-9x=7x-280\)

\(\Rightarrow648+280=7x+9x\)

\(\Rightarrow928=16x\)

\(\Rightarrow x=928:16\)

\(\Rightarrow x=58\)

Vậy \(x=58.\)

Chúc bạn học tốt!

\(\frac{x}{7}=\frac{y}{5}\Rightarrow\frac{x^2}{7}=\frac{xy}{5}=\frac{40}{5}=8\)

\(\Rightarrow x^2=56\)

\(\Rightarrow x=\sqrt{56}=2\sqrt{14}\Rightarrow y=2\sqrt{14}:7\times5=\frac{10\sqrt{14}}{7}\)

Vậy \(\left(x,y\right)=\left(2\sqrt{14},\frac{10\sqrt{14}}{7}\right)\)

Bạn ơi sai đề bài rồi nhé         

Bạn coi lại đề bài đi nhé

Dù là làm phép thử cũng ko đúng nữa

Ta có: \(-\frac{8}{15}< \frac{x}{40}\le-\frac{7}{15}\)

\(\Leftrightarrow-\frac{8.8}{15.8}< \frac{3x}{40.3}\le\frac{-7.8}{15.8}\)

\(\Leftrightarrow-\frac{64}{120}< \frac{3x}{120}\le-\frac{56}{120}\)

=> 3x từ -56 đến -63

=> 3x = -57 ; -60 ; -63

=> x = -19 ; -20 ; -21

\(\left(x-7\right)^{x+11}=\left(x-7\right)^{x+1}\)

\(\Rightarrow\left(x-7\right)^{x+11}-\left(x-7\right)^{x+1}=0\)

\(\Rightarrow\left(x-7\right)^{x+1}\left[\left(x-7\right)^{10}-1\right]=0\)

\(\Rightarrow\orbr{\begin{cases}\left(x-7\right)^{x+11}=0\\\left(x-7\right)^{10}-1=0\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x-7=0\\\left(x-7\right)^{10}=1\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=7\\x=6or\text{ }x=8\end{cases}}\)