Find the Wronskian of the set {sin 3x, cos 3x} and determine if it is linearly independent or linearly dependent. Find the Wronskian of the set {1- x, 1+x, 1-3x}

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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### Problem Statement

1. **Wronskian of Trigonometric Functions**  
   Find the Wronskian of the set \(\{\sin 3x, \cos 3x\}\) and determine if it is linearly independent or linearly dependent.

2. **Wronskian of Polynomial Functions**  
   Find the Wronskian of the set \(\{1 - x, 1 + x, 1 - 3x\}\).

### Explanation

The Wronskian is a determinant used in the study of differential equations to determine whether a set of functions is linearly independent.

Let's analyze both sets:

#### 1. **\(\{\sin 3x, \cos 3x\}\):**

- The Wronskian \(W(f, g)\) of two functions \(f(x)\) and \(g(x)\), in this case, \(\sin 3x\) and \(\cos 3x\), is given by the determinant:
  \[
  W(f, g) = \begin{vmatrix}
  f(x) & g(x) \\
  f'(x) & g'(x)
  \end{vmatrix}
  \]

- Substituting \(f(x) = \sin 3x\) and \(g(x) = \cos 3x\), we find:
  \[
  W(\sin 3x, \cos 3x) = \begin{vmatrix}
  \sin 3x & \cos 3x \\
  3\cos 3x & -3\sin 3x
  \end{vmatrix}
  \]

- Calculate the determinant:
  \[
  W = (\sin 3x)(-3\sin 3x) - (\cos 3x)(3\cos 3x) = -3\sin^2 3x - 3\cos^2 3x
  \]

- Simplify using the trigonometric identity \(\sin^2 a + \cos^2 a = 1\):
  \[
  W = -3(\sin^2 3x + \cos^2 3x) = -3 \cdot 1 = -3
  \]

- Since \(W \neq 0\), the functions \(\sin 3x
Transcribed Image Text:### Problem Statement 1. **Wronskian of Trigonometric Functions** Find the Wronskian of the set \(\{\sin 3x, \cos 3x\}\) and determine if it is linearly independent or linearly dependent. 2. **Wronskian of Polynomial Functions** Find the Wronskian of the set \(\{1 - x, 1 + x, 1 - 3x\}\). ### Explanation The Wronskian is a determinant used in the study of differential equations to determine whether a set of functions is linearly independent. Let's analyze both sets: #### 1. **\(\{\sin 3x, \cos 3x\}\):** - The Wronskian \(W(f, g)\) of two functions \(f(x)\) and \(g(x)\), in this case, \(\sin 3x\) and \(\cos 3x\), is given by the determinant: \[ W(f, g) = \begin{vmatrix} f(x) & g(x) \\ f'(x) & g'(x) \end{vmatrix} \] - Substituting \(f(x) = \sin 3x\) and \(g(x) = \cos 3x\), we find: \[ W(\sin 3x, \cos 3x) = \begin{vmatrix} \sin 3x & \cos 3x \\ 3\cos 3x & -3\sin 3x \end{vmatrix} \] - Calculate the determinant: \[ W = (\sin 3x)(-3\sin 3x) - (\cos 3x)(3\cos 3x) = -3\sin^2 3x - 3\cos^2 3x \] - Simplify using the trigonometric identity \(\sin^2 a + \cos^2 a = 1\): \[ W = -3(\sin^2 3x + \cos^2 3x) = -3 \cdot 1 = -3 \] - Since \(W \neq 0\), the functions \(\sin 3x
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