Final answer:
The given function y = 210(1.09)^x is an exponential growth function with a rate of increase of 9% per period.
Step-by-step explanation:
The function given, y = 210(1.09)^x, represents exponential growth because the base of the exponent, 1.09, is greater than 1. To identify the percentage rate of increase, we look at the base of the exponent. The base, 1.09, indicates that the quantity is increasing by 9% each period (where 'x' is the number of periods). If the base were less than 1 (for example, 0.91), it would indicate a percentage decrease and thus exponential decay.
To further illustrate this, consider a period increase in 'x'. For an increase in 'x' by 1, the function multiplies the previous value by 1.09. Therefore, the rate of increase is 9% per period.