Упростите выражение: x^18:(x^18:x^9).

\[x^{18}\ :\left( x^{18}\ :x^{9} \right) = x^{18}\ :x^{18 - 9} =\]

\[= x^{18}\ :x^{9} = x^{18 - 9} = x^{9}.\]