Is there a function whose derivative is the following matrix? If so, find it, if not, explain why not. 1 1 2 2

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
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**Question:**

Is there a function whose derivative is the following matrix? If so, find it, if not, explain why not.

\[
\begin{bmatrix}
1 & 1 \\
2 & 2 \\
\end{bmatrix}
\]

**Discussion:**

To determine if there exists a function whose derivative is this matrix, we must consider the properties of differentiable functions and their derivatives.

1. **Derivative Matrix:** 
   - A derivative matrix, or Jacobian matrix, of a function should satisfy the condition of being integrable, meaning there should exist a potential function that results in this matrix when differentiated.

2. **Criteria for Existence:**
   - For a function \( f: \mathbb{R}^n \to \mathbb{R}^m \) to have a derivative \( J \), the mixed partial derivatives must be equal. This is known as the symmetry of second derivatives or Clairaut's theorem (assuming continuity).

3. **Matrix Analysis:**
   - Given the matrix:
     \[
     \begin{bmatrix}
     1 & 1 \\
     2 & 2 \\
     \end{bmatrix}
     \]
   - The entries of a typical Jacobian are \( \frac{\partial f_1}{\partial x_1}, \frac{\partial f_1}{\partial x_2} \) for the first row and \( \frac{\partial f_2}{\partial x_1}, \frac{\partial f_2}{\partial x_2} \) for the second row.

4. **Check Symmetry:**
   - For the given matrix, check if \( \frac{\partial}{\partial x_2} (1) = \frac{\partial}{\partial x_1} (2) \).
   - Here, 1 is not equal to 2, which means \( \frac{\partial^2 f_1}{\partial x_2 \partial x_1} \neq \frac{\partial^2 f_2}{\partial x_1 \partial x_2} \).

5. **Conclusion:**
   - Since the mixed partial derivatives are not equal, the matrix cannot originate from a single differentiable function. Therefore, there is no function whose derivative is this matrix.

This type of problem helps us understand the importance of the symmetry of mixed partial derivatives
Transcribed Image Text:**Question:** Is there a function whose derivative is the following matrix? If so, find it, if not, explain why not. \[ \begin{bmatrix} 1 & 1 \\ 2 & 2 \\ \end{bmatrix} \] **Discussion:** To determine if there exists a function whose derivative is this matrix, we must consider the properties of differentiable functions and their derivatives. 1. **Derivative Matrix:** - A derivative matrix, or Jacobian matrix, of a function should satisfy the condition of being integrable, meaning there should exist a potential function that results in this matrix when differentiated. 2. **Criteria for Existence:** - For a function \( f: \mathbb{R}^n \to \mathbb{R}^m \) to have a derivative \( J \), the mixed partial derivatives must be equal. This is known as the symmetry of second derivatives or Clairaut's theorem (assuming continuity). 3. **Matrix Analysis:** - Given the matrix: \[ \begin{bmatrix} 1 & 1 \\ 2 & 2 \\ \end{bmatrix} \] - The entries of a typical Jacobian are \( \frac{\partial f_1}{\partial x_1}, \frac{\partial f_1}{\partial x_2} \) for the first row and \( \frac{\partial f_2}{\partial x_1}, \frac{\partial f_2}{\partial x_2} \) for the second row. 4. **Check Symmetry:** - For the given matrix, check if \( \frac{\partial}{\partial x_2} (1) = \frac{\partial}{\partial x_1} (2) \). - Here, 1 is not equal to 2, which means \( \frac{\partial^2 f_1}{\partial x_2 \partial x_1} \neq \frac{\partial^2 f_2}{\partial x_1 \partial x_2} \). 5. **Conclusion:** - Since the mixed partial derivatives are not equal, the matrix cannot originate from a single differentiable function. Therefore, there is no function whose derivative is this matrix. This type of problem helps us understand the importance of the symmetry of mixed partial derivatives
Expert Solution
Step 1

Yes there exist a function satisfying the 1122.

The matrix is f1x,y=x+yf2x,y=2x+2y

The function f:22

Such that 

fx,y=f1x,y,f2x,y=x+y,2x+2y

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