To simplify the expression, we can use the laws of exponents:
12a⁻⁴ b³c⁸ / 3a⁻² b⁹c⁻²
= (12/3) (a⁻⁴ / a⁻²) (b³ / b⁹) (c⁸ / c⁻²)
= 4 (a⁻⁴+2) (b³-9) (c⁸+2)
= 4a⁻² b⁻⁶ c¹⁰
Therefore, the expression is equivalent to 4a⁻² b⁻⁶ c¹⁰ for all values of a, b, and c where the expression is defined.