Implicit Differentiation, and the Chain Rule

In summary, the conversation discusses using implicit differentiation to find dy/dx, and provides an example with a trigonometric equation. The summary includes the use of the product rule and applying the n-1 rule, and clarifies the correct derivative for the example equation.
  • #1
QuarkCharmer
1,051
3

Homework Statement


Use implicit differentiation to find dy/dx
[tex]2x^3+x^2y-xy^3 = 2[/tex]

Homework Equations


Chain Rule et al.

The Attempt at a Solution



My questions is this. When deriving something like xy^3, apply the product rule to get
[tex]1y^3 + x\frac{d}{dx}y^3[/tex]

I am confused on differentiating y^3. Is it
[tex]3y^2y'[/tex]
??

Making the solution to the mentioned equation:

[tex]y' = \frac{6x^2+2xy-y^3}{3xy^2-x^2}[/tex]
 
Physics news on Phys.org
  • #2
QuarkCharmer said:

Homework Statement


Use implicit differentiation to find dy/dx
[tex]2x^3+x^2y-xy^3 = 2[/tex]

Homework Equations


Chain Rule et al.

The Attempt at a Solution



My questions is this. When deriving something like xy^3, apply the product rule to get
[tex]1y^3 + x\frac{d}{dx}y^3[/tex]

I am confused on differentiating y^3. Is it
[tex]3y^2y'[/tex]
??
Yes.
QuarkCharmer said:
Making the solution to the mentioned equation:

[tex]y' = \frac{6x^2+2xy-y^3}{3xy^2-x^2}[/tex]
The rest is pretty much just algebra.
 
  • #3
Okay, so I am bringing down the exponent, applying the n-1, then multiplying it by the derivative of the thing in the x^n (the x). I get confused because when this happens with trigonometric equations it seems different. For instance:
[tex]sin^3(sin(x^3))[/tex]

The derivative is then:
[tex]3sin^2(sinx^3)(3x^2)[/tex] ?

I am sure there should be a cosine in there somewhere.

I want to say it SHOULD be:
[tex]3sin^2(sinx^3)cos(sinx^3)cos(x^3)3x^2[/tex]

And as always, thank you.
 
  • #4
QuarkCharmer said:
Okay, so I am bringing down the exponent, applying the n-1, then multiplying it by the derivative of the thing in the x^n (the x). I get confused because when this happens with trigonometric equations it seems different. For instance:
[tex]sin^3(sin(x^3))[/tex]

The derivative is then:
[tex]3sin^2(sinx^3)(3x^2)[/tex] ?
No.
QuarkCharmer said:
I am sure there should be a cosine in there somewhere.
Yes.
You should get
[tex]3sin^2(sin(x^3))cos(x^3)(3x^2)[/tex]

That cosine factor I added is the derivative of sin(x3) with respect to x3. The 3x2 factor at the end is the derivative of x3 with respect to x.
QuarkCharmer said:
I want to say it SHOULD be:
[tex]3sin^2(sinx^3)cos(sinx^3)cos(x^3)3x^2[/tex]

And as always, thank you.
 

FAQ: Implicit Differentiation, and the Chain Rule

1. What is implicit differentiation?

Implicit differentiation is a method of finding the derivative of an equation that cannot be easily solved for one variable. It is used when an equation contains both dependent and independent variables, making it difficult to isolate the variable to be differentiated.

2. How is implicit differentiation different from explicit differentiation?

Explicit differentiation is used when the equation is already solved for the variable to be differentiated, while implicit differentiation is used when the equation is not explicitly solved for the variable. In implicit differentiation, the chain rule is applied to find the derivative of the dependent variable.

3. What is the chain rule?

The chain rule is a formula used to find the derivative of a composition of functions. It states that the derivative of the outer function multiplied by the derivative of the inner function. In the context of implicit differentiation, the chain rule is used to find the derivative of the dependent variable in an equation with multiple variables.

4. When is the chain rule used in implicit differentiation?

The chain rule is used in implicit differentiation when the dependent variable in an equation is not explicitly solved for. It is applied to find the derivative of the dependent variable by treating it as the outer function and the independent variable as the inner function.

5. Can implicit differentiation be used to find higher order derivatives?

Yes, implicit differentiation can be used to find higher order derivatives by applying the chain rule repeatedly. Each time the chain rule is applied, the resulting derivative is multiplied by the derivative of the inner function. This process can be repeated for as many times as necessary to find the desired order of derivative.

Back
Top