\(a)x\left(x^2-5\right)-\left(x^3-4x\right)=220.\\ \Leftrightarrow x^3-5x-x^3+4x=220.\\ \Leftrightarrow x=-220.\\ b)\left(4x-1\right)x^2=9\left(4x-1\right).\\ \Leftrightarrow\left(4x-1\right)\left(x^2-9\right)=0.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{1}{4}.\\x=\pm3.\end{matrix}\right.\)
\(c)\dfrac{x}{x^2-16}+\dfrac{1}{x+4}=\dfrac{3}{x-4}\left(x\ne\pm4\right).\)
\(\Leftrightarrow\dfrac{x}{x^2-16}+\dfrac{1}{x+4}-\dfrac{3}{x-4}=0.\\ \Leftrightarrow\dfrac{x+x-4-3x-12}{\left(x-4\right)\left(x+4\right)}=0.\\ \Rightarrow-x=16.\\ \Leftrightarrow x=-16.\)
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