Final answer:
To rewrite the expression 4^5 x 4^8 using each base only once, we can combine the exponents to get 4^13.
Step-by-step explanation:
To rewrite the expression 4^5 x 4^8 using each base only once, we can combine the exponents since the bases are the same. Adding the exponents gives us 4^(5+8) = 4^13.