Final answer:
The expression 4⁻⁹ × 4⁵ simplifies to 1/256.
Step-by-step explanation:
The expression 4⁻⁹ × 4⁵ can be simplified by applying the rule for multiplying powers with the same base. When you multiply two powers with the same base, you add the exponents.
Therefore, 4⁻⁹ × 4⁵ is equal to 4⁻⁹+⁵ which simplifies to 4⁻⁴. In scientific notation, 4⁻⁴ can be written as 1/4⁴ or 1/256.
So the correct expression that is equal to 4⁻⁹ × 4⁵ is A: 4⁻⁵ / 4⁹.