\(a,\frac{x}{4}=\frac{4}{x}\)

\(\Leftrightarrow x.x=4.4\)

\(x^2=16\)

\(\Leftrightarrow x=\pm4\)

\(b,\frac{x+7}{15}=-\frac{24}{36}\)

\(\frac{x+7}{15}=-\frac{2}{3}\)

\(\Leftrightarrow3\left(x+7\right)=-2.15\)

\(\Leftrightarrow3x+21=-30\)

\(\Leftrightarrow3x=-51\)

\(\Leftrightarrow x=27\)

\(c,\frac{x+1}{8}=\frac{2}{x+1}\)

\(\Leftrightarrow\left(x+1\right)\left(x+1\right)=2.8\)

\(\left(x+1\right)^2=16\)

\(\left(x+1\right)^2=\pm4^2\)

\(\Rightarrow x+1=4ho\text{ặc}x+1=-4\)

               \(x=3\)               \(x=-5\)

Vậy ....

\(d,\frac{2x-1}{\left(-3\right)^2}=\frac{\left(-3\right)^2}{2x-1}\)

\(\Leftrightarrow\left(2x-1\right)\left(2x-1\right)=\left(-3\right)^2.\left(-3\right)^2\)

\(\left(2x-1\right)^2=\pm9^2\)

\(\Leftrightarrow2x-1=9;2x-1=-9\)

               \(2x=10\)      \(2x=-8\)

                 \(x=5\)           \(x=-4\)

Vậy ...

5% nhá

\(\frac{-5}{6}+\frac{8}{3}+\frac{29}{-6}< x< \frac{-1}{2}+2+\frac{5}{2}\)

\(\Leftrightarrow\frac{-5}{6}+\frac{16}{6}+\frac{-29}{6}< x< \frac{-1}{2}+\frac{4}{2}+\frac{5}{2}\)

\(\Leftrightarrow\frac{-18}{6}< x< \frac{8}{2}\)

\(\Leftrightarrow-3< x< 4\)

\(\Leftrightarrow x\in\left\{-2;-1;0;1;2;3\right\}\)

`Answer:`

Để `A` là phân số `<=>n-7\ne0`

`=>n\ne0+7`

`=>n\ne7`

Vậy `A` là phân số khi `n\ne7`