# Write an exponential equation from this data (data table included)

by bigmac
Tags: data, equation, exponential, included, table, write
 P: 16 1. The problem statement, all variables and given/known data - The following table gives the population of a city over time: 2. Relevant equations I know this equation: y = a(b)x and exponential growth: b = 1 + growth rate and b = 1 - decay rate 3. The attempt at a solution I know from back in chapter 2 that first differences = linear model, second differences are the same = quadratic and if the 3rd differences are the same then its a cubic model...but that doesn't work here. I am completely stuck....how do I find the model. Any hints/tips/methods will be greatly appreciated!! Thanks!!
 PF Patron Sci Advisor Thanks Emeritus P: 38,412 There are two unknown constants in your formula, a and b. You need two equations to solve for two unknowns so pick two points (typically, it is best to endpoints, here 1954 and 1994). That will give you $$132459= ab^{1954}$$ and $$514013= ab^{1994}$$ It should be easy to see that dividing one equation by the other will eliminate a, leaving a single equation to solve for b.
 PF Patron HW Helper Thanks P: 6,747 Perhaps you are supposed to find a best least squares fit to the data?

 Related Discussions Introductory Physics Homework 3 General Engineering 8 Engineering, Comp Sci, & Technology Homework 1 Introductory Physics Homework 1 Computing & Technology 13