Differential Equations and population

Bogus_Roads
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Homework Statement



Consider a population p of field mice that grows at a rate proportional to the current population, so that dp/dt=rp.

Find the rate constant r if the population doubles in 30 days.

Find r if the population doubles in N days.

Homework Equations



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The Attempt at a Solution



This is the first time I've seen differential equations, and I have no idea how to do this problem, which appears to be relatively easy. If the population doubles in 30 days, then the rate of change of the population is 2P(0)/30, right? So does this mean I have to solve for P(t)--we haven't really even talked about solving anything yet.
 
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Well, this is fortunately a pretty easy differential equation to solve. Just multiply both sides by dt and then divide both sides by p. You should be able to integrate both sides then.
 
Gotcha. Thanks.
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
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