a/\(\dfrac{1}{x-4}=\dfrac{1}{4}\)(ĐKXĐ: \(x\ne4\))
\(\Rightarrow x-4=4\)
\(\Rightarrow x=8\)
b/\(\dfrac{x^2+2x}{x+2}=\dfrac{5}{4}\)(ĐKXĐ: \(x\ne-2\))
\(\Rightarrow\dfrac{x\left(x+2\right)}{x+2}=\dfrac{5}{4}\)
\(\Rightarrow x=\dfrac{5}{4}\)
c/\(\dfrac{3-x}{x^2-5x+6}=\dfrac{1}{8}\)(ĐKXĐ: \(x\ne2;x\ne3\))
\(\Rightarrow\dfrac{3-x}{\left(x^2-3x\right)-\left(2x-6\right)}=\dfrac{1}{8}\)
\(\Rightarrow\dfrac{3-x}{x\left(x-3\right)-2\left(x-3\right)}=\dfrac{1}{8}\)
\(\Rightarrow\dfrac{3-x}{\left(x-3\right)\left(x-2\right)=\dfrac{1}{8}}\)
\(\Rightarrow\dfrac{3-x}{-\left(3-x\right)\left(x-2\right)}=\dfrac{1}{8}\)
\(\Rightarrow\dfrac{1}{-x+2}=\dfrac{1}{8}\)
\(\Rightarrow-x+2=8\)
\(\Rightarrow x=-6\)
