Answer:
5^8
Explanation:
Diego added the exponents. This was an error. If he was simplifying
5^2 × 5^4, then he could add the exponents and get a correct answer. But his problem had a power raised to a power. In this case, you multiply the exponents to simplify.
(5^2)^4 means
5^2×5^2×5^2×5^2
which is
5×5×5×5×5×5×5×5
which is 5^8.