To simplify the expression \( r^{-4} p^{-8} \), we can apply the property of negative exponents, which states that \( x^{-a} = \frac{1}{x^a} \).
Using this property, we can rewrite the expression:
\[ r^{-4} p^{-8} = \frac{1}{r^4} \cdot \frac{1}{p^8} = \frac{1}{r^4 p^8} \]
Thus, the simplified form of the expression \( r^{-4} p^{-8} \) is:
\[ \frac{1}{r^4 p^8} \]