To simplify \( y^{-9} \cdot y^{-3} \cdot y^{-5} \), you can use the rule of exponents that states \( a^m \cdot a^n = a^{m+n} \).
First, add the exponents:
\[ -9 + (-3) + (-5) = -9 - 3 - 5 = -17 \]
Now you can write it as a single term:
\[ y^{-9} \cdot y^{-3} \cdot y^{-5} = y^{-17} \]
If you want to express it without a negative exponent, you can write:
\[ y^{-17} = \frac{1}{y^{17}} \]
So, the fully simplified form is:
\[ \frac{1}{y^{17}} \]