Which equation represents an exponential decay function

By definition, an exponential equation is of the form:
 
 Where,
 A: initial amount
 b: rate of change
 x: independent variable
 y: dependent variable
 For this case we have two options:
 0 <b <1: the function decreases
 b> 1: the function grows.
 Therefore, an exponential function that decreases is:
 
 Where,
 0 <b <1
 
 
 0 <b <1