To find \( f(-6) \) given the function \( f(x) = -x^2 - 13 \), we can substitute \( -6 \) into the function.
\[ f(-6) = -(-6)^2 - 13 \]
Now, calculate \( (-6)^2 \):
\[ (-6)^2 = 36 \]
Substitute this back into the equation:
\[ f(-6) = -36 - 13 \]
Now, calculate \( -36 - 13 \):
\[ -36 - 13 = -49 \]
Thus, the value of \( f(-6) \) is:
\[ f(-6) = -49 \]