5^-9/4^-12=

To solve this expression, we can simplify the exponents first:

5^(-9)/(4^(-12))

Flip the fractions to avoid negative exponents:

(4^12)/(5^9)

Raise both sides to the power of 1/12 to get rid of the exponent on 4:

[(4^12)^(1/12)]/[5^9]

Simplify the exponents:

4^(12/12)/5^9

Since 12/12 equals 1, we have:

4^1/5^9

Now, the remaining exponents are 1 on 4 and 9 on 5:

4/5^9

Therefore, the simplified expression is 4/5^9.