Find Derivative of V(u): (a-pX/q)^B

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In summary, the author is trying to find the derivative of V(u) with respect to x, but they are confused about the advice they were given. First, they solved px+cy=T to get y in terms of x. Then, they tried to use the chain rule to find U'(X,Y), but ended up getting (ax)+(by)*(-px) instead. Finally, they solved y(x) back into V and used the product rule to find the derivative of ((T-px)/c)^b.
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Homework Statement



I need to find the derivative of V(u) with respect to x

V(u)=((a-pX)/q)^B

Homework Equations



f(x)=aX^b ==> f'(x)=baX^b-1

The Attempt at a Solution



I wanted to distribute the B throughout and then I would have got -BpX^B-1, but I know this isn't doable. What I really need to know is how to deal with the entire function raised to a power. Once I get the function by itself (not raised to power B) I can get through it. Thanks for your help!
 
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  • #2
Do you know the chain rule?
 
  • #3
Take q outside of the denominator and treat it as constant. This should help you visualize the rest.
 
  • #4
I'm a little confused about the advice I got, let me write out the entire problem (I'm going to change the signs).

U(x,y)=(X^a)(Y^b).

Secondly, pX+cY=T

This is the given information.

First, I solved px+cy=T to get y in terms of x:

Y=(T-px)/c

NOW, should I use the chain rule to find U'(X,Y):

U'(x,y)=(ax)+(by)*(dy/dx)

=(ax)+(by)*(-px)

OR plug y(x) back into the U function like I did originally and solve:

U(x,y)=(x^a)((T-px)/c)^b?

If this second option is the case, how would I go about solving ((T-px)/c)^b? If I took c out of the denominator it'd be like this right: (T-px+(c^-1))^b. If this is the case, I am still having a hard time with what the derivative would be with the power b outside the equation. Thanks again.
 
  • #5
I should probably note the objective is to find U'(x,y), set it equal to zero and solve for X and Y.
 
  • #6
3.141592654 said:
I'm a little confused about the advice I got, let me write out the entire problem (I'm going to change the signs).

U(x,y)=(X^a)(Y^b).

Secondly, pX+cY=T

This is the given information.
I don't see how this has anything to do with the original problem! And what exactly is the question here? You have given us two equations. What are we to do with them?

First, I solved px+cy=T to get y in terms of x:

Y=(T-px)/c

NOW, should I use the chain rule to find U'(X,Y):

U'(x,y)=(ax)+(by)*(dy/dx)

=(ax)+(by)*(-px)

OR plug y(x) back into the U function like I did originally and solve:

U(x,y)=(x^a)((T-px)/c)^b?
Oh, I see. Well, you "expand" that right part without knowing what b is. Use the product rule on the whole thing and the chain rule on the right. The derivative of ((T-px)/c)^b is b((T-px)/c)^(b-1) times the derivative of (T- px)/c.

If this second option is the case, how would I go about solving ((T-px)/c)^b? If I took c out of the denominator it'd be like this right: (T-px+(c^-1))^b. If this is the case, I am still having a hard time with what the derivative would be with the power b outside the equation. Thanks again.
 
  • #7
Alright thanks. So just to be clear, say I had a function: f(x)=2/(x-1).

f(x)=2/(x-1) =2(x-1)^-1, so:

f'(x)=(-2(x-1)^-2)*1

Is this always true when x is part of a function and that function is to the power of any number, such as f(x)=2(x-1)^-1? If so, can anyone explain in basic terms the reason for needing to find the derivative of the entire function as well and of x? Thanks again for all your help!
 

1. What is the purpose of finding the derivative of V(u): (a-pX/q)^B?

The purpose of finding the derivative of a function is to determine its rate of change, or how much it is changing at a specific point. This can be useful in various applications, such as optimization, physics, and engineering.

2. How do I find the derivative of V(u): (a-pX/q)^B?

To find the derivative of a function, you can use the power rule, which states that for a function of the form f(x) = x^n, the derivative is f'(x) = nx^(n-1). In this case, you would apply the power rule to the term (a-pX/q)^B and then use the chain rule to take the derivative of the entire function.

3. What is the chain rule and how is it applied in finding the derivative of V(u): (a-pX/q)^B?

The chain rule is a formula used to find the derivative of a composite function, which is a function that is composed of two or more functions. To apply the chain rule, you would first take the derivative of the outer function, then multiply it by the derivative of the inner function.

4. Can you provide an example of finding the derivative of V(u): (a-pX/q)^B?

Sure, let's say we have the function V(u) = (3-u^2)^4. First, we would apply the power rule to the term (3-u^2)^4, which would give us 4(3-u^2)^3. Then, we would use the chain rule to take the derivative of the entire function, which would give us V'(u) = 4(3-u^2)^3(-2u). This can be simplified to V'(u) = -8u(3-u^2)^3.

5. What are some real-world applications of finding the derivative of V(u): (a-pX/q)^B?

Finding the derivative of a function can be applied in many fields, such as economics, physics, and engineering. For example, in economics, the derivative can be used to determine the maximum profit for a company by finding the point where the derivative is equal to zero. In physics, the derivative can be used to calculate the velocity and acceleration of an object. In engineering, the derivative can be used to determine the slope of a curve, which is important in designing structures and machines.

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