A function f and a point P are given. Let 0 correspond to the direction of the directional derivative. Complete parts a. through e. + 2y²), P ( 3.- √5) f(x,y)= In (1+6x² +2 (Type your answer alans. Type all exact answer is a comma separate answers as itu.) What angles are associated with the direction of zero change? C (Type your answer in radians. Type an exact answer in terms of . Use a comma to separate answers as needed.) c. Write the directional derivative at P as a function of 0; call this function g(0). g(0) = (Simplify your answer. Type an exact answer, using radicals as needed.) d. Find the value of 0 between 0 and 2x that maximizes g(0) and find the maximum value. What value of 0 maximizes g(0)? 0= (Type your answer in radians. Type an exact answer in terms of .) What is the maximum value? g(0) = (Type an exact answer, using radicals as needed.) e. Verify that the value of 0 that maximizes g corresponds to the direction of the gradient. Verify that the maximum value of g equals the magnitude of the gradient. Are the values from part d consistent with the values from parts a and b? O No Yes

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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# Directional Derivative Problem

A function \( f \) and a point \( P \) are given. Let \( \theta \) correspond to the direction of the directional derivative. Complete parts a through e.

## Function and Point
\[ f(x, y) = \ln \left( 1 + 6x^2 + 2y^2 \right), \quad P\left( \frac{4}{5}, -\sqrt{5} \right) \]

---

### a. Direction of Zero Change

What angles are associated with the direction of zero change?

\[ \boxed{} \]

*Type your answer in radians. Provide an exact answer in terms of \(\pi\). Use a comma to separate answers as needed.*

---

### b. Directional Derivative Function

Write the directional derivative at \( P \) as a function of \( \theta \); call this function \( g(\theta) \).

\[ g(\theta) = \boxed{} \]

*Simplify your answer. Type an exact answer, using radicals as needed.*

---

### c. Maximize \( g(\theta) \)

Find the value of \( \theta \) between 0 and \( 2\pi \) that maximizes \( g(\theta) \) and find the maximum value. What value of \( \theta \) maximizes \( g(\theta) \)?

\[ \theta = \boxed{} \]

*Type your answer in radians. Provide an exact answer in terms of \(\pi\).*

What is the maximum value?

\[ g(\theta) = \boxed{} \]

*Type an exact answer, using radicals as needed.*

---

### d. Verification

Verify that the value of \( \theta \) that maximizes \( g \) corresponds to the direction of the gradient. Verify that the maximum value of \( g \) equals the magnitude of the gradient. Are the values from part d consistent with the values from parts a and b?

- \(\circ\) No
- \(\circ\) Yes

--- 

This exercise explores the application of directional derivatives and gradients, which are fundamental concepts in multivariable calculus, critical for understanding changes in various directions on a surface represented by a function.
Transcribed Image Text:# Directional Derivative Problem A function \( f \) and a point \( P \) are given. Let \( \theta \) correspond to the direction of the directional derivative. Complete parts a through e. ## Function and Point \[ f(x, y) = \ln \left( 1 + 6x^2 + 2y^2 \right), \quad P\left( \frac{4}{5}, -\sqrt{5} \right) \] --- ### a. Direction of Zero Change What angles are associated with the direction of zero change? \[ \boxed{} \] *Type your answer in radians. Provide an exact answer in terms of \(\pi\). Use a comma to separate answers as needed.* --- ### b. Directional Derivative Function Write the directional derivative at \( P \) as a function of \( \theta \); call this function \( g(\theta) \). \[ g(\theta) = \boxed{} \] *Simplify your answer. Type an exact answer, using radicals as needed.* --- ### c. Maximize \( g(\theta) \) Find the value of \( \theta \) between 0 and \( 2\pi \) that maximizes \( g(\theta) \) and find the maximum value. What value of \( \theta \) maximizes \( g(\theta) \)? \[ \theta = \boxed{} \] *Type your answer in radians. Provide an exact answer in terms of \(\pi\).* What is the maximum value? \[ g(\theta) = \boxed{} \] *Type an exact answer, using radicals as needed.* --- ### d. Verification Verify that the value of \( \theta \) that maximizes \( g \) corresponds to the direction of the gradient. Verify that the maximum value of \( g \) equals the magnitude of the gradient. Are the values from part d consistent with the values from parts a and b? - \(\circ\) No - \(\circ\) Yes --- This exercise explores the application of directional derivatives and gradients, which are fundamental concepts in multivariable calculus, critical for understanding changes in various directions on a surface represented by a function.
**Title: Analyzing Directional Derivatives in Multivariable Functions**

---

**Problem Statement:**

A function \( f \) and a point \( P \) are given. Let \(\theta\) correspond to the direction of the directional derivative. Complete parts a through e.

Given:
\[ f(x, y) = \ln(1 + 6x^2 + 2y^2) \]
Point \( P = \left(\frac{4}{5}, -\sqrt{5}\right) \)

---

**a. Find the gradient and evaluate it at \( P \).**

- The gradient at \( P \) is \( \boxed{\phantom{x}, \phantom{x}} \).

---

**b. Find the angles \(\theta\) (with respect to the positive x-axis) between 0 and \(2\pi\) associated with the directions of maximum increase, maximum decrease, and zero change.**

1. **What angles are associated with the direction of maximum increase?**

   \(\boxed{\phantom{x}}\)

   (Type your answer in radians. Type an exact answer in terms of \(\pi\). Use a comma to separate answers as needed.)

2. **What angles are associated with the direction of maximum decrease?**

   \(\boxed{\phantom{x}}\)

   (Type your answer in radians. Type an exact answer in terms of \(\pi\). Use a comma to separate answers as needed.)

3. **What angles are associated with the direction of zero change?**

   \(\boxed{\phantom{x}}\)

   (Type your answer in radians. Type an exact answer in terms of \(\pi\). Use a comma to separate answers as needed.)

---

**c. Write the directional derivative at \( P \) as a function of \(\theta\); call this function \( g(\theta) \).**

- \( g(\theta) = \boxed{\phantom{x}} \)

  (Simplify your answer. Type an exact answer, using radicals as needed.)

---

**d. Find the value of \(\theta\) between 0 and \(2\pi\) that maximizes \( g(\theta) \) and find the maximum value. What value of \(\theta\) maximizes \( g(\theta) \)?**

---

**Explanation of Concepts:**

1. **Gradient (\(\nabla f\)):
Transcribed Image Text:**Title: Analyzing Directional Derivatives in Multivariable Functions** --- **Problem Statement:** A function \( f \) and a point \( P \) are given. Let \(\theta\) correspond to the direction of the directional derivative. Complete parts a through e. Given: \[ f(x, y) = \ln(1 + 6x^2 + 2y^2) \] Point \( P = \left(\frac{4}{5}, -\sqrt{5}\right) \) --- **a. Find the gradient and evaluate it at \( P \).** - The gradient at \( P \) is \( \boxed{\phantom{x}, \phantom{x}} \). --- **b. Find the angles \(\theta\) (with respect to the positive x-axis) between 0 and \(2\pi\) associated with the directions of maximum increase, maximum decrease, and zero change.** 1. **What angles are associated with the direction of maximum increase?** \(\boxed{\phantom{x}}\) (Type your answer in radians. Type an exact answer in terms of \(\pi\). Use a comma to separate answers as needed.) 2. **What angles are associated with the direction of maximum decrease?** \(\boxed{\phantom{x}}\) (Type your answer in radians. Type an exact answer in terms of \(\pi\). Use a comma to separate answers as needed.) 3. **What angles are associated with the direction of zero change?** \(\boxed{\phantom{x}}\) (Type your answer in radians. Type an exact answer in terms of \(\pi\). Use a comma to separate answers as needed.) --- **c. Write the directional derivative at \( P \) as a function of \(\theta\); call this function \( g(\theta) \).** - \( g(\theta) = \boxed{\phantom{x}} \) (Simplify your answer. Type an exact answer, using radicals as needed.) --- **d. Find the value of \(\theta\) between 0 and \(2\pi\) that maximizes \( g(\theta) \) and find the maximum value. What value of \(\theta\) maximizes \( g(\theta) \)?** --- **Explanation of Concepts:** 1. **Gradient (\(\nabla f\)):
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