To simplify the expression \((1/4)^9\) using the power rules for exponents, we can write it as:
\[ (1/4)^9 = (4^{-1})^9 \]
Now, applying the power of a power rule, which states \((a^m)^n = a^{m \cdot n}\), we get:
\[ (4^{-1})^9 = 4^{-1 \cdot 9} = 4^{-9} \]
Thus, the simplified expression in exponential form is:
\[ \boxed{4^{-9}} \]