Differential Equation dx/dt = k(a-x)(b-x)

In summary, the conversation discusses how to solve the differential equation dx/dt = k(a-x)(b-x), with the initial condition x(0) = 0. The attempt at a solution involves integrating using partial fractions, but the integration is incorrect and the rule of thumb for factoring is mentioned.
  • #1
mjbc
4
0

Homework Statement



dx/dt = k(a-x)(b-x)

x(0)=0

The Attempt at a Solution



dx/((a-x)(b-x)) = kdt

Integral (dx/(ab-bx-ax+x^2)) = kt +C

x/ab - (1/b)ln|x| - (1/a)ln|x| - (x^-1) = kt + C

however, if i try to substitute x(0) = 0, i get the ln 0

please help i have no idea if i am doing this right
 
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  • #2
I don't think the integration dx is correct at all. Use partial fractions.
 
  • #3
mjbc said:

Homework Statement



dx/dt = k(a-x)(b-x)

x(0)=0

The Attempt at a Solution



dx/((a-x)(b-x)) = kdt

Integral (dx/(ab-bx-ax+x^2)) = kt +C

x/ab - (1/b)ln|x| - (1/a)ln|x| - (x^-1) = kt + C

however, if i try to substitute x(0) = 0, i get the ln 0

please help i have no idea if i am doing this right

NO, 1/(a+ bx+ cx2) is NOT equal to 1/a+ 1/bx+ 1/cx2.

Rule of thumb: since it is harder to factor than to multiply, NEVER multiply terms that are already factored! (Well, almost never.)

Integrate dx/((a-x)(b-x))= dx/((x-a)(x-b) using partial fractions.
 

1. What is the meaning of the variables in the equation dx/dt = k(a-x)(b-x)?

The variable x represents the quantity being measured, such as the amount of a substance in a chemical reaction. t represents time. k, a, and b are constants that determine the rate of change and equilibrium points of the system.

2. How is this differential equation different from other equations?

This is a first-order, non-linear differential equation, meaning that the highest power of x is 1 and it is not directly proportional to t. It is also an autonomous equation, as the right-hand side does not explicitly depend on t.

3. What is the significance of the solution to this equation?

The solution to this equation represents the behavior of a system over time, such as the concentration of a chemical in a reaction or the population of a species. It can also help predict the stability and equilibrium points of the system.

4. How is this equation used in real-world applications?

Differential equations are used in various fields of science, engineering, and economics to model the behavior of complex systems. This specific equation can be used to study chemical reactions, population dynamics, and other systems with changing quantities over time.

5. What are some methods for solving this type of differential equation?

Some common methods for solving this type of differential equation include separation of variables, substitution, and Euler's method. More advanced techniques such as Laplace transforms and numerical methods may also be used.

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