Chapter 10: Problem 27
Solve the given initial-value problem up to the evaluation of a convolution integral. $$y^{\prime \prime}-2 y^{\prime}+10 y=\cos 2 t, \quad y(0)=0, \quad y^{\prime}(0)=1$$
Short Answer
Expert verified
The solution to the given initial-value problem is:
\[y(t) = -\frac{1}{10}e^{t}\cos(4t) + \frac{1}{2} e^{t}\sin(4t) + \frac{1}{10}\cos(2t) + \frac{1}{5}\sin(2t)\]
Step by step solution
01
Solve the Complementary Equation
First, we need to solve the homogeneous equation:
\[
y^{\prime \prime} - 2 y^{\prime} + 10y = 0
\]
The characteristic equation for this differential equation is
\[
r^2 - 2r + 10 = 0
\]
Solving the above quadratic equation using the quadratic formula, \(r = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\), we get complex conjugate roots
\[
r_{1,2} = \frac{2 \pm i \sqrt{32}}{2} = 1 \pm 4i
\]
Thus, the complementary solution is given by
\[
y_c(t) = C_1e^{t} \cos(4t) + C_2 e^{t} \sin(4t)
\]
02
Find the Particular Solution
Next, we will find the particular solution. Since the forcing term is \(\cos(2t)\), we will assume a particular solution of the form
\[
y_p(t) = A\cos(2t) + B\sin(2t)
\]
Now, we need to find the first and second derivatives of \(y_p(t)\):
\[
y^{\prime}_p(t) = -2A\sin(2t) + 2B\cos(2t)
\]
\[
y^{\prime\prime}_p(t) = -4A\cos(2t) - 4B\sin(2t)
\]
Substitute \(y_p(t), y^{\prime}_p(t),\) and \(y^{\prime\prime}_p(t)\) into the given non-homogeneous equation:
\[
-4A\cos(2t) - 4B\sin(2t) - 2(-2A\sin(2t) + 2B\cos(2t)) + 10( A\cos(2t) + B \sin(2t) ) = \cos(2t)
\]
Now, combining like terms, we have:
\[
(-4A + 4B + 10A)\cos(2t) + (-4B - 4A + 10B)\sin(2t) = \cos(2t)
\]
Equating the coefficients, we get the following system of equations:
\[
6A + 4B = 1
\]
\[
-4A + 6B = 0
\]
Solving the system, we find \(A = \frac{1}{10}\) and \(B = \frac{1}{5}\). Thus, the particular solution is:
\[
y_p(t) = \frac{1}{10}\cos(2t) + \frac{1}{5}\sin(2t)
\]
03
Apply the Initial Conditions
Now we need to apply the initial conditions \(y(0) = 0\) and \(y^{\prime}(0) = 1\) to find the values of \(C_1\) and \(C_2\). The general solution is the sum of the complementary and particular solutions:
\[
y(t) = y_c(t) + y_p(t) = C_1e^{t}\cos(4t) + C_2 e^{t}\sin(4t) + \frac{1}{10}\cos(2t) + \frac{1}{5}\sin(2t)
\]
Applying the first initial condition \(y(0) = 0\), we get:
\[
0 = C_1 + \frac{1}{10}
\]
So, \(C_1 = -\frac{1}{10}\).
Now we need to apply the second initial condition, \(y^{\prime}(0) = 1\). First, let's find the derivative of our general solution:
\[
y^{\prime}(t) = -\frac{1}{10}e^{t}\cos(4t) - 4 C_2 e^{t}\cos(4t) - 2 \frac{1}{10}\sin(2t) + 2 \frac{1}{5}\cos(2t)
\]
Applying the condition \(y^{\prime}(0) = 1\), we have:
\[
1 = -\frac{1}{10} -\frac{1}{5} => C_2 = \frac{1}{2}
\]
The values of \(C_1\) and \(C_2\) are now determined, and the particular solution is:
\[
y(t) = -\frac{1}{10}e^{t}\cos(4t) + \frac{1}{2} e^{t}\sin(4t) + \frac{1}{10}\cos(2t) + \frac{1}{5}\sin(2t)
\]
Now we have found the required solution for the given initial value problem, and further evaluation using convolution integral will not be performed as per the exercise prompt.
Unlock Step-by-Step Solutions & Ace Your Exams!
-
Full Textbook Solutions
Get detailed explanations and key concepts
-
Unlimited Al creation
Al flashcards, explanations, exams and more...
-
Ads-free access
To over 500 millions flashcards
-
Money-back guarantee
We refund you if you fail your exam.
Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!
Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Initial Value Problem
An initial value problem is a type of differential equation that comes with specific conditions known as initial conditions. These are the values of the function and possibly its derivatives at a certain point, often where the independent variable equals zero. This situation is a vital aspect in dynamical systems, where the entire future behavior of the solution might be determined by these initial parameters.
Consider the equation given in the exercise:
Consider the equation given in the exercise:
- Differential Equation: \(y'' - 2y' + 10y = \cos 2t\)
- Initial Conditions: \(y(0) = 0\) and \(y'(0) = 1\)
Complementary Solution
The complementary solution involves solving the homogeneous version of the differential equation, where the right-hand side is zero. For our equation, the associated homogeneous differential equation is \[ y'' - 2y' + 10y = 0. \] Solving this gives us the complementary solution. It captures the part of the solution to the differential equation that doesn't get altered by the non-homogeneous part (the right-hand side, here \(\cos 2t\)). To solve, we often find the characteristic equation:
- Characteristic Equation: \(r^2 - 2r + 10 = 0\)
- \(y_c(t) = C_1 e^t \cos(4t) + C_2 e^t \sin(4t)\)
Particular Solution
Following the complementary solution, we find the particular solution. This deals with the non-homogeneous part of the differential equation, i.e., the forcing function, which is \(\cos 2t\) in this problem. A particular solution satisfies the entire non-homogeneous differential equation, incorporating this right-hand side.
We guess a form that resembles the forcing function and calculate the coefficients by plugging back into the full equation. Here, we assume \[y_p(t) = A \cos(2t) + B \sin(2t)\] Subsequently, we take its derivatives and substitute them back into the original differential equation, equating coefficients to solve for \(A\) and \(B\). This yields:
We guess a form that resembles the forcing function and calculate the coefficients by plugging back into the full equation. Here, we assume \[y_p(t) = A \cos(2t) + B \sin(2t)\] Subsequently, we take its derivatives and substitute them back into the original differential equation, equating coefficients to solve for \(A\) and \(B\). This yields:
- \(A = \frac{1}{10}\)
- \(B = \frac{1}{5}\)
Quadratic Formula
The quadratic formula is a crucial tool in finding the roots of quadratic equations like the characteristic equation we encountered when finding the complementary solution. The formula is \[r = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\], where the equation is written in the standard form \(ax^2 + bx + c = 0\).
Applying the quadratic formula to our characteristic equation \(r^2 - 2r + 10 = 0\) gives us:
Applying the quadratic formula to our characteristic equation \(r^2 - 2r + 10 = 0\) gives us:
- \(a = 1\), \(b = -2\), \(c = 10\)