Troubleshooting Initial Value Problems for Differential Equations

In summary, the conversation was about solving an initial value problem with the equation y' = tan(x), given the initial condition y (pi/4) = 3. One person provided their attempted solution, y = sec^2(x) + 5/2, while the book's answer was y = 3 - ln(sqrt(2) cos(x)). There was a discussion about where the mistake was made, with one person suggesting a substitution and another person providing their own solution. In the end, it was determined that the original solution was incorrect and the correct answer was y = 3 - ln(cos(x) sqrt(2)).
  • #1
robbondo
90
0

Homework Statement


Solve the Given initial value problem

Homework Equations



[tex] y' = tan ( x ), y ( pi / 4 ) = 3 [/tex]

The Attempt at a Solution



Well I got the answer

[tex] y = sec^2 ( x ) + 5 / 2 [/tex]

The books answer is

[tex] y = 3 - ln (sqrt(2) cos(x) ) [/tex]

Where did I got wrong? Or is the book screwed up?
 
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  • #2
you integrated wrong, i don't know how they got sqrt(2) but you need to change tan(x) to sin(x)/cos(x) and do a substitution to get the log
 
  • #3
What do YOU believe is the integral of tan(x)??
 
  • #4
I am no expert, but I get the books answer, based on y=- ln (cos x)+C, and C =3 - ln[(sqrt2) /2)] , which = 3+ ln (sqrt 2).

Or y=-ln (cos x) -ln ( sqrt 2 ) +3

y= - ln [ (cos x) sqrt 2] +3

Dont bet your life on it. Jim
 
  • #5
sheesh... I differentiated instead of integrated. It's been a long summer. Thanks for your time guys, appreciate it.
 

FAQ: Troubleshooting Initial Value Problems for Differential Equations

What is an initial value differential equation?

An initial value differential equation is a mathematical equation that expresses the relationship between a function and its derivative, with an initial condition (or starting point) provided. It is commonly used to model real-world phenomena and predict their behavior over time.

How is an initial value differential equation solved?

There are various methods for solving initial value differential equations, including separation of variables, integrating factors, and the method of undetermined coefficients. In some cases, numerical methods may also be used.

What is the importance of initial value differential equations?

Initial value differential equations are essential in understanding and predicting the behavior of many natural and physical systems, such as population growth, chemical reactions, and electrical circuits. They also have applications in engineering, economics, and other fields.

What is the difference between an initial value differential equation and a boundary value differential equation?

The main difference between these two types of differential equations is the type of conditions provided. In an initial value differential equation, only the starting point is given, while in a boundary value differential equation, conditions are given at multiple points.

What are some real-life examples of initial value differential equations?

Some examples of real-world phenomena that can be modeled using initial value differential equations include radioactive decay, the spread of diseases, and the motion of a pendulum. Other examples include the growth of bacteria in a petri dish and the charging and discharging of a capacitor in an electrical circuit.

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