Find xf^7(x)''(0): Chain Rule Explanation

In summary, using the chain rule and product rule, we can find the second derivative of xf^7(x) as 7f^5(x)(xf(x)f''(x)+2f(x)f'(x)+6xf'^2(x)). Evaluating this at x=0 will give us the final solution.
  • #1
needOfHelpCMath
72
0
Assume we known that f(0) = 1 and f'(0)=2
Find \(\displaystyle xf^7(x)''(0)\)

Will chain rule work here?

is the \(\displaystyle u=xf^7\)

and \(\displaystyle y = u^7\)

I don't know if I am going in the right direction.
 
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  • #2
needOfHelpCMath said:
Assume we known that f(0) = 1 and f'(0)=2
Find \(\displaystyle xf^7(x)''(0)\)

Will chain rule work here?

is the \(\displaystyle u=xf^7\)

and \(\displaystyle y = u^7\)

I don't know if I am going in the right direction.
As you have noticed, this is an ambiguously worded question. I think that what it is asking for is \(\displaystyle \frac {d^2}{dx^2}\bigl(x(f(x))^7\bigr)\) (evaluated at $x=0$).
 
  • #3
Opalg said:
As you have noticed, this is an ambiguously worded question. I think that what it is asking for is \(\displaystyle \frac {d^2}{dx^2}\bigl(x(f(x))^7\bigr)\) (evaluated at $x=0$).

this is what I got from solving the problem:

For the first derivative

\(\displaystyle d/dx[f^7x^8]\)
\(\displaystyle f^7*d/dx[x^8]\)
\(\displaystyle 8f^7x^7\)Second derivative:

\(\displaystyle d/dx8f^7x^7\)
\(\displaystyle 8f^7*d/dx[x^7]\)
\(\displaystyle =8*7x^6f^7\)
\(\displaystyle 56f^7x^6\)
 
  • #4
I would let:

\(\displaystyle g(x)=xf^7(x)\)

Differentiate w.r.t $x$, using the product and chain rules:

\(\displaystyle g'(x)=x(7f^6(x)f'(x))+(1)f^7(x)=7xf^6(x)f'(x)+f^7(x)=f^6(x)(7xf'(x)+f(x))\)

Now, differentiate again:

\(\displaystyle g''(x)=f^6(x)(7xf''(x)+7f'(x)+f'(x))+6f^5(x)f'(x)(7xf'(x)+f(x))=f^5(x)(f(x)(7xf''(x)+8f'(x))+6f'(x)(7xf'(x)+f(x)))\)

\(\displaystyle g''(x)=7f^5(x)(xf(x)f''(x)+2f(x)f'(x)+6xf'^2(x))\)

Now, can you find $g''(0)$?
 

FAQ: Find xf^7(x)''(0): Chain Rule Explanation

1. What is the chain rule in calculus?

The chain rule is a rule in calculus that is used to find the derivative of a composite function. It 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.

2. How do you use the chain rule to find xf^7(x)''(0)?

To use the chain rule to find xf^7(x)''(0), you first need to identify the inner and outer functions. In this case, the inner function is x and the outer function is f^7(x). Then, you take the derivative of the outer function, which is 7f^6(x) times the derivative of the inner function, which is 1. So, the final answer is 7xf^6(x).

3. Why do we need the chain rule to find xf^7(x)''(0)?

We need the chain rule to find xf^7(x)''(0) because it is a composite function, meaning it is made up of two or more functions. The derivative of a composite function cannot be found simply by taking the derivative of each individual function, so the chain rule allows us to find the derivative of the composite function.

4. Can the chain rule be applied to any composite function?

Yes, the chain rule can be applied to any composite function. As long as the function is made up of two or more functions, the chain rule can be used to find its derivative.

5. Are there any other important rules in calculus related to finding derivatives?

Yes, there are other important rules in calculus related to finding derivatives, such as the product rule, quotient rule, and power rule. These rules are used to find the derivative of more complex functions that cannot be solved using the basic derivative rules.

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