Final answer:
The expression 9² = 81 is represented in logarithmic form as log₉ 81 = 2, which corresponds to option a, since 9 raised to the power of 2 equals 81.
Step-by-step explanation:
The logarithmic form of the expression 9² = 81 can be represented as log₉ 81 = 2. This is because the definition of a logarithm is the exponent to which the base (in this case, 9) must be raised to produce the number (in this case, 81). In logarithmic form, we are essentially asking, "To what power must we raise 9 to get 81?" Because 9 raised to the power of 2 equals 81, the correct logarithmic form is option a: log₉ 81 = 2.