Implicit differentiation

In summary: So the derivative of 5y^2 is 4x + 3/4x and then 2y(dy)/(dx) = what the right side equals thru using the quotient rule.
  • #1
Jan Hill
63
0

Homework Statement


Given 5y^2 = 4x - 3/4x + 3


Homework Equations


is it permissable to say this is equal to y^2 = 4x -3 /5(4x + 3) and then 2y(dy)/(dx) = what the right side equals thru using the quotient rule?

I know the answer is dy/dx = 12/5y(4x + 3)^2 but I don't know how to get that



The Attempt at a Solution

 
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  • #2
How do you not know how to get it? You just said how! Use the quotient rule on the RHS.
 
  • #3
I'll explain, since apparently the person above me doesn't believe in clarifying?
[PLAIN]http://img101.imageshack.us/img101/3676/step1a.gif

Since this equation is comprised of simple polynomials you will be able to differentiate each term by itself.

Using the power rule and remembering how to apply implicit differentiation via. the Chain Rule:
[PLAIN]http://img585.imageshack.us/img585/1932/step2a.gif becomes [PLAIN]http://img87.imageshack.us/img87/9609/step2b.gif

To differentiate a single x with a constant in front, it just becomes the constant due to the power rule, so 4x becomes 4.

Instead of using the quotient rule for -3/4x I would put (4x)^-1 on top and multiply that by -3, so that you can use the power rule instead (which is 99% of the time much easier to deal with).
(-1)*(-3) = 3 and then reduce the power by 1 and you end up with (3(4x)^-2) which can be rewritten as (3)/(4x^2).

The derivative of any constant is zero, 3 is a constant therefore you can just ignore it.

So far we have:
[PLAIN]http://img59.imageshack.us/img59/8198/step3.gif

So we can just solve for y' by dividing both sides by 10y, if we decided to maybe add fractions on the other side then clean things up with some algebra we get:
[PLAIN]http://img41.imageshack.us/img41/6554/step4.gif

So... apparently the answer you "know" ... is wrong? Wolfram Alpha agrees with me:
http://www.wolframalpha.com/input/?i=derivative+of+5y^2+%3D+4x+-+3%2F4x+%2B+3

Hope this helped!
 
Last edited by a moderator:
  • #4
First you aren't supposed to give someone a complete answer. Second you entered it in wrong to wolfram, they most likely meant (4x – 3)/(4x + 3) not 4x – (3/4x) + 3. And what further clarification is needed? They stated exactly how to solve this problem and then said I don’t know what to do. If they got stuck on the quotient rule they need to show their work, not just be given an answer.
 
  • #5
JonF said:
How do you not know how to get it? You just said how! Use the quotient rule on the RHS.

You were right the 4x and 3 term are inside the brackets
 

1. What is implicit differentiation?

Implicit differentiation is a mathematical technique used to differentiate a function that is defined implicitly by an equation. This means that the equation does not explicitly express one variable in terms of the other, making it difficult to differentiate using traditional methods.

2. How is implicit differentiation different from explicit differentiation?

Explicit differentiation involves differentiating a function that is expressed explicitly in terms of one variable. Implicit differentiation, on the other hand, involves differentiating a function that is defined implicitly by an equation, where one variable is not explicitly expressed in terms of the other.

3. When is implicit differentiation useful?

Implicit differentiation is useful when differentiating functions that cannot be expressed explicitly in terms of one variable, such as curves or surfaces defined by implicit equations. It is also useful in cases where the derivative of a function is needed, but the function is too complex to differentiate using traditional methods.

4. What is the process for performing implicit differentiation?

The process for implicit differentiation involves treating the dependent variable as a function of the independent variable, and then using the chain rule to differentiate both sides of the equation with respect to the independent variable. The resulting equation can then be solved for the derivative of the dependent variable.

5. What are some common mistakes to avoid when using implicit differentiation?

One common mistake when using implicit differentiation is forgetting to apply the chain rule when differentiating the dependent variable. It is also important to correctly identify the dependent and independent variables in the equation. Additionally, care must be taken when solving for the derivative, as it may involve both the dependent and independent variables.

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