To rewrite the expression \( 5^{-9} \cdot 4^{-12} \) using positive exponents only, we can apply the property of negative integer exponents, which states that \( a^{-n} = \frac{1}{a^n} \).
Thus, we can rewrite each term as follows:
\[ 5^{-9} = \frac{1}{5^9} \] \[ 4^{-12} = \frac{1}{4^{12}} \]
Now we can combine these expressions:
\[ 5^{-9} \cdot 4^{-12} = \frac{1}{5^9} \cdot \frac{1}{4^{12}} = \frac{1}{5^9 \cdot 4^{12}} \]
So, the equivalent expression using only positive exponents is:
\[ \frac{1}{5^9 \cdot 4^{12}} \]