What equation is equivalent to 9x - 3 = 729?

Rewrite 9 as 3², so 9ˣ becomes (3²)ˣ = 3²ˣ. Also, 729 = 3⁶. Therefore, 9ˣ − 3 = 729 is equivalent to 3²ˣ − 3 = 3⁶, which is choice D.

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