How Can We Determine ∂z/∂r for a Complex Multivariable Equation?

  • Thread starter catch22
  • Start date
In summary, using the chain rule, the partial derivative ∂z/∂r can be found by multiplying the partial derivatives of z with respect to its variables x and y, which are expressed in terms of w and t, and then multiplying those with the partial derivatives of w and t with respect to r. The final answer is correct regardless of the variables used, but it may be more conventional to express it in terms of u and r.
  • #1
catch22
62
0

Homework Statement



If z= x2 - y2 + xy
x = w + 4t
y = w2 -5t + 4
w = r2 - 5u
t = 3r + 5u

find ∂z/∂r

Homework Equations

The Attempt at a Solution


This is going to be quite long and tedious so bare with me, but here is my work.
drawing a diagram to help out a bit.

upload_2015-11-6_2-33-2.png
∂z/∂r = (∂z/∂x)(∂x/∂w)(∂w/∂r) + (∂z/∂x)(∂x/∂t)(∂t/∂r) + (∂z/∂y)(∂y/∂w)(∂w/∂r) + (∂z/∂y)(∂y/∂t)(∂t/∂r)

=(2x-y)(1)(2r) + (2x-y)(4)(3) + (-2y+x)(2w)(2r) + (-2y + x)(-5)(3)

now is that the final answer? or should everything be in terms of r?
 

Attachments

  • upload_2015-11-6_2-28-14.png
    upload_2015-11-6_2-28-14.png
    1.3 KB · Views: 369
  • upload_2015-11-6_2-32-55.png
    upload_2015-11-6_2-32-55.png
    1.3 KB · Views: 367
Physics news on Phys.org
  • #2
I haven't checked your final differentiations, but if they are correct then the answer will be equally correct regardless of the variables in terms of which it is expressed. It may however be more conventional to express it in terms of u and r, since they are the 'ultimate' parameters. It comes down to what you think your teacher will want. If you don't know then it would be safer to express it in terms of u and r.
 
  • Like
Likes catch22

FAQ: How Can We Determine ∂z/∂r for a Complex Multivariable Equation?

1. What is the meaning of ∂z/∂r?

∂z/∂r is a mathematical notation that represents the partial derivative of the function z with respect to the variable r. It measures the rate of change of z in relation to a small change in the variable r.

2. How do you solve for ∂z/∂r?

To solve for ∂z/∂r, you need to use the rules of partial differentiation. First, identify the function z and the variable r. Then, treat all other variables (x, y, w, t) as constants and differentiate the function with respect to r. This will result in an expression for ∂z/∂r.

3. What is the purpose of solving for ∂z/∂r?

Solving for ∂z/∂r allows us to understand the relationship between the function z and the variable r. It also helps in finding the maximum or minimum values of a function and in analyzing changes in a system.

4. Can you provide an example of solving for ∂z/∂r?

Sure, let's say we have the function z = x^2 + y^3 + w^2t. To solve for ∂z/∂r, we treat x, y, w, and t as constants and differentiate the function with respect to r. This would result in ∂z/∂r = 2w^2t.

5. Are there any tips for solving for ∂z/∂r?

When solving for ∂z/∂r, it is important to clearly identify the function and the variable of interest. It's also helpful to remember the rules of partial differentiation, such as the product rule and chain rule. Additionally, practice and familiarizing yourself with different types of functions can improve your understanding and skills in solving for ∂z/∂r.

Back
Top