Find the derivative of the function(chain rule)

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In summary, the conversation discusses finding the derivative of f(x+g(x)) at x=0 using the chain rule and the given values of f(x), f'(x), g(x), and g'(x). After some confusion and incorrect attempts, it is determined that the correct answer is 12. The conversation ends with a suggestion to revise differentiation.
  • #1
youngstudent16
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Homework Statement


Various values of the functions f(x) and g(x) and their derivatives are given in the table below. Find the derivative of f(x+g(x)) at x=0.

at x=0 f(x)=5 f'(x)=2 g(x)=1 g'(x)=3
at x=1 f(x)=7 f'(x)=3 g(x)=-2 g'(x)=-5
2. Homework Equations
Chain rule

The Attempt at a Solution



So f'(x)(x+g(x))[(1+g'(x))(f(x)]
2(0+1)(1+3)(5)=40

Is this correct or did I overlook something chain rule always has a way of making me feel I missed something [/B]
 
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  • #2
Could you detail the chain rule used? Just the base formula.
 
  • #3
Derivative of the outside multiplied by the derivative of the inside
(f*g)'=(f'*g)+(g'*f)

Where f=f(x)
g=(x+g(x))

I'm getting 40 but not sure if I attempted this correctly
 
  • #4
youngstudent16 said:
Derivative of the outside multiplied by the derivative of the inside
(f*g)'=(f'*g)+(g'*f)

Where f=f(x)
g=(x+g(x))

I'm getting 40 but not sure if I attempted this correctly
I asked as this did not seem the right chain rule use. If i understood the problem correctly.
One issue is that f(x+g(x)) is not equal to f*(x+g(x)).
f(u) is a function and in your case u=x+g(x).
What chain rule do you need to apply in this case?
 
  • #5
youngstudent16 said:
So f'(x)(x+g(x))[(1+g'(x))(f(x)]
2(0+1)(1+3)(5)=40
This has been written wrong .

d( f(x+g(x)) )/dx = f'(x+g(x))*(1+g'(x)) .
 
  • #6
Qwertywerty said:
This has been written wrong .

d( f(x+g(x)) )/dx = f'(x+g(x))*(1+g'(x)) .
Ahhhh. Much better.
And now, just solve :P
 
  • #7
Qwertywerty said:
This has been written wrong .

d( f(x+g(x)) )/dx = f'(x+g(x))*(1+g'(x)) .

f'(x+g(x))
How do I solve this with the given information? Would it just be the derivative f a constant which makes the whole thing 0?
 
  • #8
youngstudent16 said:
f'(x+g(x))
How do I solve this with the given information? Would it just be the derivative f a constant which makes the whole thing 0?
Well you don't know anything about the function f, but solving for x=0 does just mean f'(0+g(0)).
 
  • #9
youngstudent16 said:
Would it just be the derivative f a constant which makes the whole thing 0?
I don't follow you .
 
  • #10
Qwertywerty said:
I don't follow you .
I would plug in the value for x and g(0) getting derivative of 1 which is 0. Making the final answer 0.

I think that's right I really confused myself on the chain rule
 
  • #11
youngstudent16 said:
I would plug in the value for x and g(0) getting derivative of 1 which is 0. Making the final answer 0.

I think that's right I really confused myself on the chain rule
but f'(1) is not zero by the conditions above.
 
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  • #12
Sorry about the mixed responses to both of you. I have been switching through screens all morning.
 
  • #13
youngstudent16 said:
I would plug in the value for x and g(0) getting derivative of 1 which is 0. Making the final answer 0
You don't find derivative by putting the value before differentiating .
 
  • #14
Lok said:
but f'(1) is not zero by the conditions above.

oh wow that x=1 did come in handy I got it finally 12 was correct

thanks for the patience really helped with my confusion
 
  • #15
youngstudent16 said:
oh wow that x=1 did come in handy I got it finally 12 was correct

thanks for the patience really helped with the my confusion
My suggestion to you is that you revise differentiation once again .
 
Last edited:
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  • #16
Anytime there is any time :P.
 

1. What is the chain rule and why is it important in finding derivatives?

The chain rule is a formula used to find the derivative of a composite function. It is important because many functions in mathematics and science are composed of multiple functions, and the chain rule allows us to find the rate of change of these composite functions.

2. How do you apply the chain rule in finding derivatives?

To apply the chain rule, you must first identify the inner and outer functions of the composite function. Then, you take the derivative of the outer function and multiply it by the derivative of the inner function, treating the inner function as a variable.

3. Can you provide an example of using the chain rule to find a derivative?

For example, if we have the function f(x) = (x^2 + 1)^3, we can rewrite it as f(x) = g(h(x)) where g(x) = x^3 and h(x) = x^2 + 1. To find the derivative of f(x), we would use the chain rule: f'(x) = g'(h(x)) * h'(x) = 3(x^2 + 1)^2 * 2x = 6x(x^2 + 1)^2.

4. Are there any special cases or exceptions when using the chain rule?

Yes, there are some special cases where the chain rule may need to be modified. For example, if the outer function is a logarithmic or exponential function, we must use the chain rule with the natural logarithm or exponential function respectively.

5. How can the chain rule be applied in real-world scenarios?

The chain rule has many real-world applications, such as in physics and engineering. For example, in physics, the chain rule can be used to find the velocity of an object with changing acceleration, or the rate of change of a temperature with respect to time in thermodynamics. It is also used in economics and finance to find the marginal cost and marginal revenue of a business.

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