To find \( f(-4) \) for the function \( f(x) = \left( \frac{x}{8} \right)^2 \), we can substitute \(-4\) into the function:
\[ f(-4) = \left( \frac{-4}{8} \right)^2 \]
First, simplify the fraction:
\[ \frac{-4}{8} = -\frac{1}{2} \]
Now, square this value:
\[ f(-4) = \left( -\frac{1}{2} \right)^2 = \frac{1}{4} \]
Thus, the final answer is:
\[ f(-4) = \frac{1}{4} \]