Find Taylor Series for 1/x Around x=3

In summary: So you can write the Taylor series as ##f(x) = \sum_{n=0}^\infty \frac{f^{(n)}(3)}{n!}(x-3)^n##.In summary, to find the Taylor series for f(x)=1/x about a center of 3, you need to evaluate the derivatives of f(x) at x = 3 and plug them into the general formula for a Taylor series. This will give you the series: ##1/x = \sum_{n=0}^\infty \frac{(-1)^n}{2^n}(x-3)^n##.
  • #1
soitgoes2019
2
0

Homework Statement


Find the Taylor Series for f(x)=1/x about a center of 3.

Homework Equations

The Attempt at a Solution


f'(x)=-x^-2
f''(x)=2x^-3
f'''(x)=-6x^-4
f''''(x)=24x^-5
...
f^n(x)=-1^n * (x)^-(n+1) * (x-3)^n
I'm not sure where I went wrong...
 
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  • #2
How did you write the sum, i.e. the requested Taylor series? And what is wrong or why do you think it is wrong?
 
  • #3
I wrote the sum from n=0 to ∞ as: ∑-1^n (x)^-(n+1) (x-3)^n
I'm not sure if that is correctly centered at 3
 
  • #4
As far as I can see, there is only a minor error; however crucial to the usage of Taylor series. You should check the general formula again.

Edit: And your formula for ##f^{(n)}## is wrong. You must not drop the coefficients all of a sudden, only because they might cancel out later in the calculation.
 
  • #5
soitgoes2019 said:

Homework Statement


Find the Taylor Series for f(x)=1/x about a center of 3.

Homework Equations

The Attempt at a Solution


f'(x)=-x^-2
f''(x)=2x^-3
f'''(x)=-6x^-4
f''''(x)=24x^-5
...
f^n(x)=-1^n * (x)^-(n+1) * (x-3)^n
I'm not sure where I went wrong...

When you expand ##f(x)## about ##x = 3## your coefficients involve ##f^{(n)}(3)##, not ##f^{(n)}(x)##. But, of course, you compute ##f^{(n)}(3)## by first computing ##f^{(n)}(x)## and then setting ##x = 3##.
 

1. How do you find the Taylor series for 1/x around x=3?

To find the Taylor series for 1/x around x=3, you can use the formula: f(x) = f(a) + f'(a)(x-a) + (f''(a)/2!)(x-a)^2 + ... + (f^n(a)/n!)(x-a)^n. In this case, a=3 and f(x)=1/x. So, the Taylor series for 1/x around x=3 becomes: 1/3 - (1/9)(x-3) + (2/81)(x-3)^2 - (5/729)(x-3)^3 + ... + ((-1)^n*n!)/3^(n+1)(x-3)^n.

2. What is the purpose of finding the Taylor series for 1/x around x=3?

The purpose of finding the Taylor series for 1/x around x=3 is to approximate the function 1/x near the point x=3. This can be useful in situations where the exact value of the function may be difficult to calculate, but an approximation is sufficient.

3. Can the Taylor series for 1/x around x=3 be used for any value of x?

No, the Taylor series for 1/x around x=3 is only valid for values of x that are close to 3. As the distance from x=3 increases, the accuracy of the approximation decreases.

4. How many terms should be used in the Taylor series for 1/x around x=3?

The number of terms needed in the Taylor series for 1/x around x=3 depends on the desired level of accuracy. Generally, the more terms used, the more accurate the approximation will be.

5. Can the Taylor series for 1/x around x=3 be used to find the exact value of 1/x?

No, the Taylor series for 1/x around x=3 is an approximation and will never yield the exact value of 1/x. However, as more terms are added, the approximation will become closer to the exact value.

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