Final answer:
The equivalent expression to 5^12 x 5^8 is 25^20.
Step-by-step explanation:
To find the equivalent expressions to 5^12 x 5^8, we need to apply the rule that when multiplying two numbers with the same base, we add the exponents together. In this case, the base is 5 and the exponents are 12 and 8.
So, 5^12 x 5^8 can be simplified to 5^(12+8) = 5^20.
Therefore, the equivalent expression to 5^12 x 5^8 is A. 25^20.