Using chain rule to obtain the derivative dz/dt

I'm not sure what your question is, but in summary, the conversation is about verifying a solution for a problem involving the chain rule and finding ##\frac{dz}{dt}## using given equations and terms. The original attempt at a solution is then compared to the answer provided by the teacher.
  • #1
catch22
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Homework Statement


upload_2015-11-2_22-26-2.png


Homework Equations


dz/dt = dz/dx⋅dx/dt + dz/dy⋅dy/dt

The Attempt at a Solution


[/B]
I am getting :

=[-sin(x+7y) ⋅ 10t] + [-sin(x+7y) ⋅ 7 ⋅ (-1/ t2)]

then changing x and y terms:

=[-sin((5t2)+7(1/t)) ⋅ 10t] + [-sin((5t2)+7(1/t)) ⋅ 7 ⋅ (-1/ t2)]
 
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  • #2
catch22 said:

Homework Statement


View attachment 91274

Homework Equations


dz/dt = dz/dx⋅dx/dt + dz/dy⋅dy/dt

The Attempt at a Solution


[/B]
I am getting :

=[-sin(x+7y) ⋅ 10t] + [-sin(x+7y) ⋅ 7 ⋅ (-1/ t2)]

then changing x and y terms:

=[-sin((5t2)+7(1/t)) ⋅ 10t] + [-sin((5t2)+7(1/t)) ⋅ 7 ⋅ (-1/ t2)]

Do you have a question?
 
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  • #3
Ray Vickson said:
Do you have a question?
yes, sorry, I'm just verifying If I had done it correctly.
the answer my teacher posted was :
upload_2015-11-2_23-20-31.png

which really got me questioning myself.
 
  • #4
It seems that you teacher has ##x(t)=5t^4##
 
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1. What is the chain rule?

The chain rule is a mathematical rule that allows us to find the derivative of a function that is composed of two or more other functions. It is used when we have a function within another function.

2. How do you use the chain rule to obtain the derivative dz/dt?

To use the chain rule to find dz/dt, we first need to identify the composition of functions, where z is a function of t and t is a function of another variable. Then, we take the derivative of the outer function with respect to the inner function, multiplied by the derivative of the inner function with respect to the independent variable.

3. What is the purpose of using the chain rule to obtain the derivative dz/dt?

The purpose of using the chain rule is to find the rate of change of a dependent variable with respect to an independent variable, when the dependent variable is a function of another variable. It allows us to calculate the instantaneous rate of change for more complex functions.

4. What are some examples of using the chain rule to obtain the derivative dz/dt?

An example of using the chain rule to find the derivative dz/dt could be in the context of physics, where z represents the position of an object at time t, and t is a function of time. Another example could be in economics, where z represents the cost of a product at time t, and t is a function of the quantity of the product.

5. Are there any common mistakes when using the chain rule to obtain the derivative dz/dt?

One common mistake when using the chain rule is not properly identifying the composition of functions. It is also important to remember to take the derivative of the outer function with respect to the inner function, and then multiply by the derivative of the inner function with respect to the independent variable. Another mistake is not simplifying the final expression, which can lead to incorrect results.

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