Change in x (Differentiation) - Calc III needed?

In summary, the conversation is about finding dx/dt and dy/dt, and properly applying the chain rule in solving for these values in a given equation. The correct answer is D.
  • #1
Qube
Gold Member
468
1

Homework Statement



http://i.minus.com/jDtSwpCGlrMhP.jpg

Homework Equations



Solving for dx/dy (change in x with respect to y) I get a solution that isn't one of the answer choices.

The Attempt at a Solution



3y^2 = 8x' + x'/x

Coordinate:

x = 1 (given)
y = 2 (solved for in original equation)

3(4) = 9x'
12/9 = dx/dy
4/3 = dx/dy (change of x with respect to y).
 
Last edited by a moderator:
Physics news on Phys.org
  • #2
Qube said:

Homework Statement



http://i.minus.com/jDtSwpCGlrMhP.jpg

Homework Equations



Solving for dx/dy (change in x with respect to y) I get a solution that isn't one of the answer choices.

The Attempt at a Solution



3y^2 = 8x' + x'/x

Coordinate:

x = 1 (given)
y = 2 (solved for in original equation)

3(4) = 9x'
12/9 = dx/dy
4/3 = dx/dy (change of x with respect to y).

You want to think about dy/dt and dx/dt not dy/dx. For example, d/dt(y^3)=3y^2*dy/dt. Try that again. There is a correct answer in there.
 
Last edited by a moderator:
  • #3
No matter what derivatives you take, please make sure you apply the chain rule properly. I don't think you did that in your attempt.
 
  • #4
The tipoff that they're looking for time rates of change (dx/dt and dy/dt) is the units in the answers - units/sec.
 
  • #5
brmath said:
No matter what derivatives you take, please make sure you apply the chain rule properly. I don't think you did that in your attempt.

I'm not seeing the issue when I take the derivative of the equation with respect to y.
 
  • #6
Mark44 said:
The tipoff that they're looking for time rates of change (dx/dt and dy/dt) is the units in the answers - units/sec.

Thank you. That makes more sense. I found dx/dt and plugged in dy/dt which is -1/2.

3y^2(dy/dt) = 8(dx/dt) + dx/dt*(1/x)

y=2, as always.

3(4)(-1/2) = 9(dx/dt)

-6 = 9(dx/dt)
-2/3 = dx/dt

It appears the answer is D.
 
  • #7
Qube said:
Thank you. That makes more sense. I found dx/dt and plugged in dy/dt which is -1/2.

3y^2(dy/dt) = 8(dx/dt) + dx/dt*(1/x)

y=2, as always.

3(4)(-1/2) = 9(dx/dt)

-6 = 9(dx/dt)
-2/3 = dx/dt

It appears the answer is D.

Yes, it is.
 

1. What is differentiation and why is it important?

Differentiation is a mathematical operation that measures the rate at which one quantity changes with respect to another quantity. It is important in many fields of science, including physics, engineering, and economics, as it allows us to analyze and understand the behavior of changing systems.

2. How is differentiation different in Calculus III compared to Calculus I and II?

In Calculus III, differentiation involves finding the partial derivatives of functions with multiple variables. This means that instead of finding the rate of change along a single axis, we are finding the rate of change along multiple axes simultaneously. This requires a deeper understanding of multivariable calculus concepts such as gradients and directional derivatives.

3. What are some real-world applications of differentiation?

Differentiation has many practical applications in fields such as physics, engineering, and economics. For example, in physics, differentiation is used to calculate the velocity and acceleration of moving objects. In economics, it is used to analyze supply and demand curves. In engineering, it is used to optimize designs and predict the behavior of complex systems.

4. Can differentiation be used to find the maximum and minimum values of a function?

Yes, differentiation can be used to find the maximum and minimum values of a function. In fact, one of the main applications of differentiation is optimization, which involves finding the maximum or minimum value of a function. This is done by setting the derivative of the function equal to zero and solving for the critical points.

5. What are some common methods for differentiating functions?

There are several methods for differentiating functions, including the power rule, product rule, quotient rule, and chain rule. The power rule is used for functions with a single variable raised to a power. The product rule is used for functions that are the product of two other functions. The quotient rule is used for functions that are the quotient of two other functions. And the chain rule is used for composite functions, where one function is nested inside another.

Similar threads

  • Calculus and Beyond Homework Help
Replies
25
Views
343
  • Calculus and Beyond Homework Help
Replies
2
Views
731
  • Calculus and Beyond Homework Help
Replies
10
Views
439
  • Calculus and Beyond Homework Help
Replies
3
Views
902
  • Calculus and Beyond Homework Help
Replies
8
Views
760
  • Calculus and Beyond Homework Help
Replies
21
Views
839
  • Calculus and Beyond Homework Help
Replies
4
Views
811
  • Calculus and Beyond Homework Help
Replies
1
Views
825
  • Calculus and Beyond Homework Help
Replies
6
Views
1K
  • Calculus and Beyond Homework Help
Replies
3
Views
2K
Back
Top