The computed values for \( f(x) \) are:
- \( f(0.9) = -510.0000 \)
- \( f(0.99) = -50099.9999 \)
- \( f(0.999) = -5000999.9999 \)
- \( f(0.9999) = -500010000.0001 \)
Thus, the final boxed answers are:
\[
\boxed{f(0.9) = -510.0000}
\]
\[
\boxed{f(0.99) = -50099.9999}
\]
\[
\boxed{f(0.999) = -5000999.9999}
\]
\[
\boxed{f(0.9999) = -500010000.0001}
\]