81 дробь x минус x дробь x

[latex] \frac{81}{x}- \frac{x}{x}=1 \\ \\ \frac{81-x}{x}-1=0 \\ \\ \frac{81-x-x}{x}=0 \\ \\ \frac{81-2x}{x}=0 \\ \\ \left \{ {{81-2x=0} \atop {x \neq 0}} \right. [/latex] x=40,5