Mathematics College

Suppose a country's population at any time t grows in accordance with the rule dP dt = kP + I where P denotes the population at any time t, k is a positive constant reflecting the natural growth rate of the population, and I is a constant giving the (constant) rate of immigration into the country. If the total population of the country at time t = 0 is P0, find an expression for the population at any time t.

Answers

Answer 1

Answer:

[tex]\mathbf{P =\bigg (P_o +\dfrac{ I}{k} \bigg)e^{kt}- \dfrac{I}{k}}[/tex]

Step-by-step explanation:

Given that:

A country population at any given time (t) is:

[tex]\dfrac{dP}{dt}= kP+I[/tex]

where;

P = population at any time t

k = positive constant

I = constant rate of immigration into the country.

Using the method of separation of the variable;

[tex]\dfrac{dP}{kP+1}= dt[/tex]

Taking integration on both sides:

[tex]\int \dfrac{dP}{kP+I}= \int \ dt[/tex]

[tex]\dfrac{1}{k} log (kP + I) = t+c_1 \ \ \ here: c_1 = constant \ of \ integration[/tex]

[tex]log (kP + I) =k t+kc_1[/tex]

By applying the exponential on both sides;

[tex]e^{log (kP + I) }=e^{k t+kc_1 }[/tex]

[tex]KP+I = e^{kt} *e^{kc_1}[/tex]

Assume [tex]e^{kc_1 }= C[/tex]

Then:

[tex]kP + I = Ce^{kt}[/tex]

[tex]kP = Ce^{kt}-I[/tex]

[tex]P =\dfrac{ Ce^{kt}-I}{k} \ \ \---- Let \ that \ be \ equation \ (1)[/tex]

When time t = 0, The Total population of the country is also [tex]P_o[/tex]

[tex]P_o = \dfrac{Ce^{0(t)} -I}{k}[/tex]

[tex]P_o = \dfrac{Ce^{0} -I}{k}[/tex]

[tex]P_o = \dfrac{C-I}{k}[/tex]

C - I = kP₀

C = kP₀ + I

Substituting the value of C back into equation(1), we have:

[tex]P =\dfrac{ (kP_o+1)e^{kt}-I}{k}[/tex]

[tex]P =\dfrac{ (kP_o+1)e^{kt}}{k} - \dfrac{I}{k}[/tex]

[tex]\mathbf{P =\bigg (P_o +\dfrac{ I}{k} \bigg)e^{kt}- \dfrac{I}{k}}[/tex]

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Answers

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Answers

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