Formula 1: f (x) = abx. Formula 2: f (x) = a (1 + r)x. Formula 3: P = P0 0 ek t. Where, x (or) t = time (time can be in years, days, (or) months, whatever you are using should be consistent throughout the problem). Note: Here, b = 1 + r ≈ e k . In exponential growth, always b > 1.