Maximize 4x+ 2 y+ 2 z
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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Question
Once I set up my lambda with either gradient I struggle with finding what point I should use in order to get my max value. If you could please show how you get your answer that would be very helpful. Thank you.

Transcribed Image Text:**Question 8**
Maximize \(4x + 2y + 2z\) on the sphere \(x^2 + y^2 + z^2 = 19\).
Options:
a) There is no maximum.
b) The maximum is \(\frac{19\sqrt{14}}{18}\).
c) The maximum is \(\frac{2\sqrt{14}}{3}\).
d) The maximum is \(-2\sqrt{114}\).
e) The maximum is \(2\sqrt{114}\).
f) None of these.
**Solution Steps:**
1. Defined function: \( f(x, y, z) = 4x + 2y + 2z \)
2. Gradient of \( f(x, y, z) = (4, 2, 2) \)
Steps involve using Lagrange multipliers:
- Define \( g(x, y, z) = x^2 + y^2 + z^2 - 19 \)
- Gradient of \( g(x, y, z) = (2x, 2y, 2z) \)
- Setting \(\nabla f = \lambda \nabla g\) leads to a system of equations:
- \( 4 = 2\lambda x \)
- \( 2 = 2\lambda y \)
- \( 2 = 2\lambda z \)
- Sphere constraint: \( x^2 + y^2 + z^2 = 19 \)
Solving the equations:
- From \( 2\lambda x = 4 \) and \( 2\lambda y = 2 \):
- \( x = 2/\lambda \)
- \( y = 1/\lambda \)
- \( z = 1/\lambda \)
- Substitute into the sphere equation to solve for \( \lambda \).
This problem involves using calculus and linear algebra concepts to find the maximum value of a linear function constrained on a sphere, illustrating applications of optimization in multivariable calculus.
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