Derivatives of Composite Functions

In summary, the conversation involves finding the derivative of y with respect to x when x = 1, given that f'(-1) = 2. The solution involves setting g(x) = x^2 + 3x - 5, rewriting y in terms of g(x), and using the chain rule to find dy/dx. It is also suggested to go back and read the problem again and use the given information of f'(-1) = 2 to solve for dy/dx.
  • #1
Dough
19
0
I just need a nudge in the rigth direction ais don't know where to start
Let y = f(x^2 + 3x - 5) find dy/dx when x = 1, given that f'(-1) = 2

Thanks!
 
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  • #2
Let g(x) = x² + 3x - 5, then y = f(g(x)). dy/dx = f'(g(x))g'(x)
 
  • #3
i am not sure what else y have to do to get the answer, i wrote that out as well as

-1 = x^2 + 3x -5
solved and got x = 1 or -3...

but what else?

dy/dx = f'(x^2 + 3x - 5)(2x + 3)
 
  • #4
Dough said:
i am not sure what else y have to do to get the answer, i wrote that out as well as
-1 = x^2 + 3x -5
solved and got x = 1 or -3...
but what else?
dy/dx = f'(x^2 + 3x - 5)(2x + 3)

I suggest going back and reading the problem again! You were asked to find y'(1). How about setting x= 1?
 
  • #5
Very good suggestion.

And just to ease your worries, you were given a good piece of information: that f'(-1)=2. Do you see where this applies to the problem?
 

What are derivatives of composite functions?

Derivatives of composite functions are a type of derivative that involves taking the derivative of a function that is composed of two or more other functions. In other words, the inner function is substituted into the outer function, and then the derivative is taken.

How do you find the derivative of a composite function?

To find the derivative of a composite function, you can use the chain rule, which states that the derivative of a composite function is equal to the derivative of the outer function multiplied by the derivative of the inner function.

Can you give an example of a composite function and its derivative?

Yes, an example of a composite function is f(x) = sin(3x), which can be rewritten as f(x) = sin(u) where u = 3x. The derivative of this function is f'(x) = 3cos(3x).

What is the purpose of finding derivatives of composite functions?

The purpose of finding derivatives of composite functions is to analyze the rate of change of a function that is composed of multiple functions. This can be useful in many areas of science, such as physics, engineering, and economics.

Are there any special cases when finding derivatives of composite functions?

Yes, there are a few special cases when finding derivatives of composite functions. For example, when the inner function is a constant, the derivative is simply the derivative of the outer function. Additionally, when the inner function is a linear function, the chain rule can be simplified.

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