Exponential Decay with Positive and Negative Initial Value

Exponential decay as a function of time with adjustable rate (0<rate<1) and initial amount (between -5 and 5). f(time) = InitialAmount * (1 - rate)^time

1. What happens at initial amount = 0? Why? 2. What happens to the shape of the graph as you increase rate? Decrease? 3. Compare and contrast the graphs when initial amount > 0 and initial amount < 0.