To simplify \( 7^{-3} \cdot 7^{-5} \) using the property of negative integer exponents, we can first use the property:
\[ a^{-n} = \frac{1}{a^n} \]
Applying this property, we have:
\[ 7^{-3} \cdot 7^{-5} = \frac{1}{7^3} \cdot \frac{1}{7^5} \]
Now, we can combine the fractions:
\[ \frac{1}{7^3} \cdot \frac{1}{7^5} = \frac{1}{7^{3+5}} = \frac{1}{7^8} \]
Thus, the expression \( 7^{-3} \cdot 7^{-5} \) can be expressed with positive exponents as:
\[ 7^{-3} \cdot 7^{-5} = \frac{1}{7^8} \]