Math Problem Statement

Use the Chain Rule to find the indicated partial derivatives. M = xe^y - z^2, x = 2uv, y = u - v, z = u + v; when u = 3, v = -1

Solution

To solve the given problem, we need to use the Chain Rule to compute the partial derivatives of MM with respect to uu and vv. Let's walk through this step by step.

Given:

M=xeyz2M = xe^y - z^2 x=2uv,y=uv,z=u+vx = 2uv, \quad y = u - v, \quad z = u + v with u=3u = 3 and v=1v = -1.

1. Compute Mu\frac{\partial M}{\partial u}

Using the Chain Rule, we can express Mu\frac{\partial M}{\partial u} in terms of the partial derivatives of MM with respect to xx, yy, and zz, and the partials of xx, yy, and zz with respect to uu.

Mu=Mxxu+Myyu+Mzzu\frac{\partial M}{\partial u} = \frac{\partial M}{\partial x} \cdot \frac{\partial x}{\partial u} + \frac{\partial M}{\partial y} \cdot \frac{\partial y}{\partial u} + \frac{\partial M}{\partial z} \cdot \frac{\partial z}{\partial u}

Let's compute each term:

  • Mx=ey\frac{\partial M}{\partial x} = e^y
  • My=xey\frac{\partial M}{\partial y} = xe^y
  • Mz=2z\frac{\partial M}{\partial z} = -2z

Now for the partials of xx, yy, and zz with respect to uu:

  • xu=2v\frac{\partial x}{\partial u} = 2v
  • yu=1\frac{\partial y}{\partial u} = 1
  • zu=1\frac{\partial z}{\partial u} = 1

Thus, the expression for Mu\frac{\partial M}{\partial u} becomes: Mu=ey2v+xey1+(2z)1\frac{\partial M}{\partial u} = e^y \cdot 2v + xe^y \cdot 1 + (-2z) \cdot 1

2. Compute Mv\frac{\partial M}{\partial v}

Similarly, for Mv\frac{\partial M}{\partial v}, we apply the Chain Rule:

Mv=Mxxv+Myyv+Mzzv\frac{\partial M}{\partial v} = \frac{\partial M}{\partial x} \cdot \frac{\partial x}{\partial v} + \frac{\partial M}{\partial y} \cdot \frac{\partial y}{\partial v} + \frac{\partial M}{\partial z} \cdot \frac{\partial z}{\partial v}

  • xv=2u\frac{\partial x}{\partial v} = 2u
  • yv=1\frac{\partial y}{\partial v} = -1
  • zv=1\frac{\partial z}{\partial v} = 1

So: Mv=ey2u+xey(1)+(2z)1\frac{\partial M}{\partial v} = e^y \cdot 2u + xe^y \cdot (-1) + (-2z) \cdot 1

Substituting u=3u = 3 and v=1v = -1

  • x=2uv=2(3)(1)=6x = 2uv = 2(3)(-1) = -6
  • y=uv=3(1)=4y = u - v = 3 - (-1) = 4
  • z=u+v=3+(1)=2z = u + v = 3 + (-1) = 2
  • ey=e4e^y = e^4

Now we substitute these values into the two equations.

For Mu\frac{\partial M}{\partial u}:

Mu=e42(1)+(6)e41+(2)(2)\frac{\partial M}{\partial u} = e^4 \cdot 2(-1) + (-6)e^4 \cdot 1 + (-2)(2) Mu=2e46e44=8e44\frac{\partial M}{\partial u} = -2e^4 - 6e^4 - 4 = -8e^4 - 4

For Mv\frac{\partial M}{\partial v}:

Mv=e42(3)+(6)e4(1)+(2)(2)\frac{\partial M}{\partial v} = e^4 \cdot 2(3) + (-6)e^4 \cdot (-1) + (-2)(2) Mv=6e4+6e44=12e44\frac{\partial M}{\partial v} = 6e^4 + 6e^4 - 4 = 12e^4 - 4

Final Answer:

Mu=8e44\frac{\partial M}{\partial u} = -8e^4 - 4 Mv=12e44\frac{\partial M}{\partial v} = 12e^4 - 4

Would you like further explanation or details on any step?

Here are some related questions for you to explore:

  1. How does the Chain Rule work in multivariable calculus?
  2. What are the applications of partial derivatives in real-world problems?
  3. How do you compute partial derivatives in more complex expressions?
  4. How does implicit differentiation differ from using the Chain Rule?
  5. What are some other techniques for finding total derivatives?

Tip: In problems involving chain rule, always break down the derivative into smaller parts by computing each derivative step-by-step for each variable and expression.

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Math Problem Analysis

Mathematical Concepts

Multivariable Calculus
Chain Rule
Partial Derivatives

Formulas

Chain Rule: ∂M/∂u = ∂M/∂x * ∂x/∂u + ∂M/∂y * ∂y/∂u + ∂M/∂z * ∂z/∂u
Chain Rule: ∂M/∂v = ∂M/∂x * ∂x/∂v + ∂M/∂y * ∂y/∂v + ∂M/∂z * ∂z/∂v

Theorems

Chain Rule for Multivariable Functions

Suitable Grade Level

University level (Calculus III or Multivariable Calculus)