Final answer:
The expression 9 x 9 x 4 x 4 x 4 x 9 x 9 x 9 can be simplified to 9^4.
Step-by-step explanation:
The expression 9 x 9 x 4 x 4 x 4 x 9 x 9 x 9 can be written in index form as 9⁄9 x 4⁄4 x 4⁄4 x 9⁄9 x 9⁄9.
Since any number raised to the power of 1 is equal to the number itself, we can remove the exponents and simplify the expression to 9 x 1 x 1 x 9 x 9.
Therefore, the simplified form is 9 x 9 x 9 x 9, which can also be written as 94.