Using the Chain Rule to Find the Derivative of a Complex Function: Homework Help

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In summary, the conversation discusses the use of L'Hospital's rule to find the derivative of a function involving the tangent function. The experts recommend transforming the function into a logarithmic form and using the limit of the natural logarithm to solve the problem.
  • #1
jpd5184
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0

Homework Statement



lim
x-o+ (tan(4x))^x

Homework Equations





The Attempt at a Solution



to get the derivative i have to use the chain rule so it would be.

lim
x- 0+ (x(tan(4x)^x-1)(sec^2(4)
 
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  • #2
Hey, jpd5184.

First you have to identify what kind of indeterminate form you have. Can you see you have the form 0^0?

To apply L'Hospital's rule, remember that you need to have [tex]\frac{0}{0}[/tex] or [tex]\frac{\pm \infty}{\pm \infty}[/tex]. What can do you do to transform this 0^0 indeterminate form to one of these? Hint: think of the log function and its properties.

Good luck.
 
  • #3
Also, although you do not need it here because you do NOT just differentiate the function itself, the derivative, with respect to x, of [itex]f(x)^x[/itex] is NOT "[itex]x f(x)^{x-1}[/itex]". The power rule only works when the power is a constant, not a function of x.
 
  • #4
would i just make tanx into sinx/cosx
 
  • #5
I don't think that would be useful to do.

For this type of problem there is a technique that is useful.
Let y = (tan(4x))x
Then ln y = x ln(tan(4x)) = tan(4x)/(1/x)

Now take the limit of both sides, and recognize that what you're getting is the limit of the ln of what you want.

Check your textbook. I'm betting that there is an example that uses this technique.
 
  • #6
thanks very much, i did learn this technique, just forgot it.
 

What is the chain rule and why is it important in finding derivatives of complex functions?

The chain rule is a calculus rule that allows us to find the derivative of a composite function. In other words, it allows us to find the rate of change of a function that is made up of other functions. It is important in finding derivatives of complex functions because many real-world problems involve functions that are composed of other functions, and the chain rule allows us to easily find the derivative of these complex functions.

How do I apply the chain rule to find the derivative of a composite function?

To apply the chain rule, you first need to identify the inner and outer functions in the composite function. Then, you can use the formula (f ∘ g)'(x) = f'(g(x)) * g'(x), where f'(x) and g'(x) are the derivatives of the inner and outer functions respectively. You will need to use the chain rule multiple times if the function is composed of more than two functions.

What are some common mistakes students make when using the chain rule?

One common mistake is forgetting to use the chain rule altogether and trying to find the derivative as if it were a simple function. Another mistake is not properly identifying the inner and outer functions, which can lead to incorrect application of the chain rule. It is also important to remember to use the product rule or quotient rule when necessary, as the chain rule only applies to composite functions.

Can the chain rule be used to find higher order derivatives of composite functions?

Yes, the chain rule can be applied to find higher order derivatives of composite functions. To find the second derivative, simply apply the chain rule again to the derivative found using the first application of the chain rule. For third and higher order derivatives, you will need to apply the chain rule multiple times, just as you would with finding the first derivative.

Are there any tips for simplifying the process of using the chain rule?

One helpful tip is to use function notation and write out the derivatives of the inner and outer functions before plugging them into the chain rule formula. This can help you keep track of the different parts and make sure you are using the correct derivative for each function. It is also important to practice and familiarize yourself with the chain rule, as it will become easier to apply with more experience.

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