Find D„f(3, 2), where u = cos(0)i + sin(0)j, using each given value of 0. (i) 4 (ii) 0 3 (iii) 0 3. (iv) Ө — 6.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
Section: Chapter Questions
Problem 1RQ
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Given the function:

f(x,y)=3-(x/3)-(y/2)

Solve the questions below, 

Thank you 

**Problem Statement:**

(b) Find \( D_{\mathbf{u}} f(3, 2) \), where \( \mathbf{u} = \cos(\theta)\mathbf{i} + \sin(\theta)\mathbf{j} \), using each given value of \( \theta \).

**Given Values of \( \theta \):**

(i) \( \theta = \frac{\pi}{4} \)

\[ \text{(Box to display result)} \]

(ii) \( \theta = \frac{2\pi}{3} \)

\[ \text{(Box to display result)} \]

(iii) \( \theta = \frac{4\pi}{3} \)

\[ \text{(Box to display result)} \]

(iv) \( \theta = -\frac{\pi}{6} \)

\[ \text{(Box to display result)} \]

**Explanation:**

For each given angle \( \theta \), determine the directional derivative \( D_{\mathbf{u}} f(3, 2) \) by substituting \( \theta \) into the unit vector formula:
\[ \mathbf{u} = \cos(\theta)\mathbf{i} + \sin(\theta)\mathbf{j} \]

Calculate the cosine and sine components of \( \mathbf{u} \) for each case and find the directional derivative using these values.
Transcribed Image Text:**Problem Statement:** (b) Find \( D_{\mathbf{u}} f(3, 2) \), where \( \mathbf{u} = \cos(\theta)\mathbf{i} + \sin(\theta)\mathbf{j} \), using each given value of \( \theta \). **Given Values of \( \theta \):** (i) \( \theta = \frac{\pi}{4} \) \[ \text{(Box to display result)} \] (ii) \( \theta = \frac{2\pi}{3} \) \[ \text{(Box to display result)} \] (iii) \( \theta = \frac{4\pi}{3} \) \[ \text{(Box to display result)} \] (iv) \( \theta = -\frac{\pi}{6} \) \[ \text{(Box to display result)} \] **Explanation:** For each given angle \( \theta \), determine the directional derivative \( D_{\mathbf{u}} f(3, 2) \) by substituting \( \theta \) into the unit vector formula: \[ \mathbf{u} = \cos(\theta)\mathbf{i} + \sin(\theta)\mathbf{j} \] Calculate the cosine and sine components of \( \mathbf{u} \) for each case and find the directional derivative using these values.
### Directional Derivative and Gradient Calculation

**(c)** Calculate \( D_u f(3, 2) \), where \( \mathbf{u} = \frac{\mathbf{v}}{\|\mathbf{v}\|} \), using each given vector \( \mathbf{v} \).

- **(i)** \( \mathbf{v} = \mathbf{i} + \mathbf{j} \)
  - [Answer Box]

- **(ii)** \( \mathbf{v} = -3\mathbf{i} - 4\mathbf{j} \)
  - [Answer Box]

- **(iii)** \( \mathbf{v} \) is the vector from (1, 2) to (-2, 6)
  - [Answer Box]

- **(iv)** \( \mathbf{v} \) is the vector from (3, 2) to (4, 5)
  - [Answer Box]

**(d)** Find \( \nabla f(x, y) \).

- \( \nabla f(x, y) = \) 
  - [Answer Box]

**(e)** Find the maximum value of the directional derivative at (3, 2).

- [Answer Box]

**(f)** Identify a unit vector \( \mathbf{u} \) orthogonal to \( \nabla f(3, 2) \) and compute \( D_u f(3, 2) \).

- \( D_u f(3, 2) = \) 
  - [Answer Box]

This section requires understanding of vector calculus, focusing on the computation of directional derivatives using various vectors.
Transcribed Image Text:### Directional Derivative and Gradient Calculation **(c)** Calculate \( D_u f(3, 2) \), where \( \mathbf{u} = \frac{\mathbf{v}}{\|\mathbf{v}\|} \), using each given vector \( \mathbf{v} \). - **(i)** \( \mathbf{v} = \mathbf{i} + \mathbf{j} \) - [Answer Box] - **(ii)** \( \mathbf{v} = -3\mathbf{i} - 4\mathbf{j} \) - [Answer Box] - **(iii)** \( \mathbf{v} \) is the vector from (1, 2) to (-2, 6) - [Answer Box] - **(iv)** \( \mathbf{v} \) is the vector from (3, 2) to (4, 5) - [Answer Box] **(d)** Find \( \nabla f(x, y) \). - \( \nabla f(x, y) = \) - [Answer Box] **(e)** Find the maximum value of the directional derivative at (3, 2). - [Answer Box] **(f)** Identify a unit vector \( \mathbf{u} \) orthogonal to \( \nabla f(3, 2) \) and compute \( D_u f(3, 2) \). - \( D_u f(3, 2) = \) - [Answer Box] This section requires understanding of vector calculus, focusing on the computation of directional derivatives using various vectors.
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