for \( f_{z} \), we have
\[
\begin{aligned}
f_{y}(x, y, z) & =f_{z}\left(\frac{y z^{2}}{x^{3}}\right)+f_{z}\left[\tan \left(2 x^{2}+4 y-z\right)\right] \\
& =f_{z}\left(y^{2} x^{-3}\right)+f_{z}\left[\tan \left(2 x^{2}+4 y-z\right)\right] \\
& =2 y z x^{-3}+\sec ^{2}\left(2 x^{2}+4 y-z\right) \cdot(-1) \\
& =\frac{2 y z}{x^{3}}-\sec ^{2}\left(2 x^{2}+4 y-z\right)
\end{aligned}
\]