Find 9th Derivative of f(x) = cos(6x^4)-1 at x=0 | Maclaurin Series Homework

In summary, the conversation discusses computing the 9th derivative of a function using the MacLaurin series. The key is to identify the term containing x^9 in the series and use the properties of cos to simplify the expression.
  • #1
demersal
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0

Homework Statement




(1 pt) Compute the 9th derivative of:
f(x) = [tex]\frac{cos(6x^4)-1}{x^7}[/tex]
at x=0.



Homework Equations



Hint: Use the MacLaurin series for f(x).

The Attempt at a Solution



I have tried many weird ways and cannot come up with the correct numerical answer. I've gotten 0 each time and it still comes up as wrong. Please help point me in the correct direction, even if it is only a verbal explanation!

Thanks so much
 
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  • #2
The only term in the expansion that would contribute to a 9th derivative would be the term containing x^9. If you look up the Maclaurin series of cos you'll it can be written as a sum of even powers of it's argument. The fourth power of 6x^4 contains an x^16. 16-7=9. Is that enough of a hint.
 
  • #3
Yes, thank you very much. I think I can work it out now!
 

Related to Find 9th Derivative of f(x) = cos(6x^4)-1 at x=0 | Maclaurin Series Homework

1. What is a Maclaurin series?

A Maclaurin series is a type of Taylor series expansion that is centered around x=0. It is used to approximate a function by representing it as an infinite sum of terms involving the function's derivatives evaluated at x=0.

2. How do you find the 9th derivative of a function?

To find the 9th derivative of a function, you need to take the derivative 9 times. Each time, you will decrease the power of x by 1 and multiply by the original function's coefficient. For example, to find the 9th derivative of f(x) = x^3, you would get f^(9)(x) = 3*2*1 = 6.

3. What is the formula for the Maclaurin series of cos(x)?

The Maclaurin series for cos(x) is given by f(x) = 1 - (x^2)/2! + (x^4)/4! - (x^6)/6! + ... = ∑((-1)^n * (x^(2n)) / (2n)!), where n ranges from 0 to infinity.

4. How do you find the Maclaurin series of a function?

To find the Maclaurin series of a function, you need to first find the derivatives of the function at x=0. Then, plug these derivatives into the Maclaurin series formula with x=0 as the center. You can continue adding terms until you see a pattern or reach the desired degree of accuracy.

5. How do you find the 9th derivative of f(x) = cos(6x^4)-1 at x=0?

To find the 9th derivative of f(x) = cos(6x^4)-1 at x=0, you will first need to use the chain rule to find the derivative of cos(6x^4). Then, you can use the power rule to find the derivatives of 6x^4 and finally, evaluate the 9th derivative at x=0. This will give you the coefficient of the 9th term in the Maclaurin series for f(x).

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