Final answer:
In an exponential decay function represented by y = ab^x, the value of b must be between 0 and 1 (0 < b < 1) to correctly depict decay.
Step-by-step explanation:
If y = abx represents an exponential decay function, the possible values of b are that 0 < b < 1. In exponential decay, the factor b represents the percent decrease if it is less than 1, but greater than 0. If b was equal to or greater than 1, or less than or equal to 0, it would not represent a decay. For example, when b = 0.5, the function halves with each increase in x. In an exponential decay function, as x increases, y decreases, which is achieved by having a base b between 0 and 1.