## Precalculus (10th Edition)

The ratio of consecutive values is not constant (because $\frac{12}{6}=2\ne\frac{18}{12}=1.5$), hence, it is not an exponential function. The difference of consecutive values is not constant (because $6-3\ne12-6$), hence it is not a linear function. Thus, the function is neither linear nor exponential.