Which necessary condition must be met in order for the product rule a^m · aⁿ = a^m+n to be considered valid?

The exponents must be identical; the rule is only used to double the power of a single exponent value.

The bases must be identical; the rule only applies when the factors share the exact same base (including signs).

The coefficients must be one; the rule fails if there are any numbers in front of the base variables.

The bases must be different; if the bases are the same, you must multiply the exponents instead of adding them.