\(y=f\left(x\right)=\dfrac{5}{x-1}\)
a) ĐKXĐ khi: \(x-1\ne0\) \(\Leftrightarrow x\ne1\)
b)
\(y=f\left(-2\right)=\dfrac{5}{-2-1}=\dfrac{5}{-\left(2+1\right)}=\dfrac{5}{-3}=\dfrac{-5}{3}\)
\(y=f\left(\dfrac{1}{3}\right)=\dfrac{5}{\dfrac{1}{3}-1}=\dfrac{5}{\dfrac{1}{3}-\dfrac{3}{3}}=\dfrac{5}{\dfrac{-2}{3}}=\dfrac{-15}{2}\)
c)
* \(y=f\left(x\right)=\dfrac{5}{x-1}=-1\)
\(\Rightarrow x-1=5:\left(-1\right)\)
\(\Rightarrow x-1=-5\)
\(\Rightarrow x=-5+1\)
\(\Rightarrow x=-\left(5-1\right)\)
\(\Rightarrow x=-4\)
Vậy \(y=-1\) thì \(x=-4\)
* \(y=f\left(x\right)=\dfrac{5}{x-1}=1\)
\(\Rightarrow x-1=5:1\)
\(\Rightarrow x-1=5\)
\(\Rightarrow x=5+1\)
\(\Rightarrow x=6\)
Vậy \(y=1\) thì \(x=6\)
* \(y=f\left(x\right)=\dfrac{5}{x-1}=\dfrac{1}{5}\)
\(\Rightarrow x-1=5:\dfrac{1}{5}\)
\(\Rightarrow x-1=5.5\)
\(\Rightarrow x-1=25\)
\(\Rightarrow x=25+1\)
\(\Rightarrow x=26\)
Vậy \(y=\dfrac{1}{5}\) thì \(x=26\)