Solve First order linear differential equation, initial conditions

In summary, a first order linear differential equation is a mathematical equation involving a function, its derivatives, and constants. It can be solved using methods such as separation of variables, integrating factor, or undetermined coefficients. Initial conditions refer to the values of the function and its derivatives at a specific point and are used to find the particular solution. An example of solving a first order linear differential equation is given, and some real-world applications include modeling in physics, biology, chemistry, and engineering.
  • #1
NCyellow
22
0

Homework Statement


The problem is given as follows:
Solve
dy/dt + y = 0.5, y(t=0)=1

Homework Equations


The Attempt at a Solution


I separate the y terms from the t terms, which gives me
dy(-y+0.5)=dt
I integrate both sides to get
-ln(-y+0.5)=t+C
C is the constant, I combine the constants from both sides to one value.
Multiplying both sides by the negative,
ln(-y+0.5)=-t-C
Now i e both sides
-y+0.5=e^(-t-C)
Therefore I can simplify to y=e^(-t-C)+0.5, which is my solution
Since y(0)=1,
e^(-C) = 0.5
I don't know what exactly I am supposed to do with that...
Was my answer correct?
Please advise, Thank you!
 
Last edited:
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  • #2
surely you mean [itex]e^{-C}=1.5[/itex]
 
  • #3
latentcorpse said:
surely you mean [itex]e^{-C}=1.5[/itex]

Wrote the signs wrong, fixed now.
 
  • #4
NCyellow said:

Homework Statement


The problem is given as follows:
Solve
dy/dt + y = 0.5, y(t=0)=1


Homework Equations





The Attempt at a Solution


I separate the y terms from the t terms, which gives me
dy(-y+0.5)=dt
dy/(-y+0.5)= dt

I integrate both sides to get
-ln(-y+0.5)=t+C
C is the constant, I combine the constants from both sides to one value.

Multiplying both sides by the negative,
ln(-y+0.5)=-t-C
Now i e both sides
-y+0.5=e^(-t-C)
Therefore I can simplify to y=e^(-t-C)+0.5, which is my solution
Since y(0)=1,
e^(-C) = 0.5
I don't know what exactly I am supposed to do with that...
Was my answer correct?
Please advise, Thank you!
[itex]-y+0.5= e^{-t-C}[/itex] is NOT equivalent to [itex]y= e^{-t-C}+0.5[/itex].

Subtracting 0.5 from each side of [itex]-y+0.5= e^{-t-C}[/itex] gives [itex]-y= e^{-t-C}- 0.5[/itex] and then, multiplying both sides by -1, [itex]y= 0.5- e^{-t-C}[/itex].

Now, taking y= 1 when t= 0, [itex]1= 0.5- e^{-C}[/itex] so [itex]e^{-C}= 0.5[/itex] still.
And [itex]e^{-t-C}= e^{-t}e^{-C}[/itex]. Since [itex]e^{-C}= 0.5[/itex], [itex]e^{-t-C}= 0.5e^{-t}[/itex] and your solution is [itex]y= 0.5- 0.5e^{-t}[/itex]
 

1. What is a first order linear differential equation?

A first order linear differential equation is a type of mathematical equation that involves a function, its derivatives, and constants. It can be written in the form of dy/dx + P(x)y = Q(x), where P(x) and Q(x) are functions of x.

2. How do you solve a first order linear differential equation?

To solve a first order linear differential equation, you can use the method of separation of variables, where you separate the variables on opposite sides of the equation and then integrate both sides. You can also use the integrating factor method or the method of undetermined coefficients.

3. What are initial conditions in a differential equation?

Initial conditions refer to the values of the function and its derivatives at a specific point, usually denoted as x = a. These values are used to find the particular solution of the differential equation.

4. Can you provide an example of solving a first order linear differential equation?

Yes, for example, let's say we have the differential equation dy/dx + 2x = 6 with initial condition y(0) = 1. Using the integrating factor method, we can rewrite the equation as (e^2x)y' + (2xe^2x)y = 6e^2x. We can then integrate both sides to get the particular solution y = 3 - 3e^-2x. Plugging in the initial condition, we get the complete solution y = 3 - 3e^-2x + e^-2x.

5. What are some real-world applications of first order linear differential equations?

First order linear differential equations have many real-world applications, such as in physics for modeling the motion of objects, in biology for studying population growth, and in chemistry for studying reaction rates. They are also used in engineering for solving problems related to electric circuits, heat transfer, and fluid dynamics.

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