\(x^2-x-18+\frac{72}{x^2-x}=0\)
\(\Leftrightarrow\frac{x^2-x-18}{1}+\frac{72}{x^2-x}=0\)
\(\Leftrightarrow\frac{x^2-x-18}{1}+\frac{72}{x.\left(x-1\right)}=0\)
\(\Leftrightarrow\frac{x.\left(x-1\right).\left(x^2-x-18\right)}{x.\left(x-1\right)}+\frac{72}{x.\left(x-1\right)}=0\)
\(\Leftrightarrow x.\left(x-1\right).\left(x^2-x-18\right)+72=0\)
\(\Leftrightarrow\left(x^2-x\right).\left(x^2-x-18\right)+72=0\)
\(\Leftrightarrow x^4-x^3-18x^2-x^3+x^2+18x+72=0\)
\(\Leftrightarrow x^4-2x^3-17x^2+18x+72=0\)
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