Concept:
Use substitution:
\[
t = x^5
\Rightarrow dt = 5x^4 dx
\]
Step 1: Rewrite integral.
\[
\int x^9 f(x^5)\,dx = \int x^5 \cdot x^4 f(x^5)\,dx
\]
Step 2: Substitute.
\[
= \int x^5 f(t) \cdot \frac{dt}{5}
= \frac{1}{5} \int t f(t)\,dt
\]
Step 3: Use integration by parts.
\[
\int t f(t)\,dt = t g(t) - \int g(t)\,dt
\]
Step 4: Back substitute.
\[
= \frac{x^5}{5} g(x^5) - \int x^4 g(x^5)\,dx
\]