Second derivatives using delta notation

In summary, the conversation discusses the formula for the second derivative of a function, which can be approximated using (f(x+h)-2f(x)+f(x-h))/h^2. It also explores the relationship between this formula and the first derivative formula, (f(x+h)-f(x-h))/2h. The conversation concludes by discussing another way to derive the formula using f''(x) and f'(x+h/2).
  • #1
bodensee9
178
0

Homework Statement



Can some one explain why the second derivative of f(x) is (f(x+h)-2f(x)+f(x-h))/h^2? If you take the intervals to be x = 0 to x = 1 and you divide up the segment into little “hs” so that each x=h, 2h, 3h, nh, and so on?

I see that first derivatives can be approximated using (f(x+h)-f(x-h))/2h, but if you were to try to measure the change in (f(x+h)-f(x-h))/2h, wouldn't you get (f(x+2h)-f(x)-f(x)-f(x-2h))/2h^2?

Thanks.
 
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  • #2
bodensee9 said:
I see that first derivatives can be approximated using (f(x+h)-f(x-h))/2h, but if you were to try to measure the change in (f(x+h)-f(x-h))/2h, wouldn't you get (f(x+2h)-f(x)-f(x)-f(x-2h))/2h^2?

No, you would get (f(x+2h)-f(x)-f(x)-f(x-2h))/4h^2

And if you substitute g = 2h you get the standard formula.

Another way to derive it is to use f''(x) is approximately (f'(x+h/2)-f'(x-h/2))/h and f'(x+h/2) is approximately (f(x+h)-f(x))/h
 
  • #3
Oh I see it now. Thanks!
 

1. What is a second derivative?

A second derivative is a mathematical concept that refers to the rate of change of the slope of a function. It is the derivative of the derivative of a function and is represented by the symbol f''(x) or d²y/dx².

2. How is the second derivative calculated using delta notation?

The second derivative can be calculated using delta notation by taking the derivative of the first derivative of a function. It is represented as Δf' = f(x+Δx) - f(x) / Δx, and then taking the derivative of this expression again using the same process.

3. What is the significance of the second derivative in calculus?

The second derivative is important in calculus because it helps us understand the concavity of a function. A positive second derivative indicates a function is concave up, while a negative second derivative indicates a function is concave down. It also helps us find maximum and minimum points on a curve.

4. Can the second derivative be negative?

Yes, the second derivative can be negative. This means that the rate of change of the slope of a function is decreasing. This is seen in concave down curves, where the slope is decreasing as x increases.

5. How can the second derivative be used to find inflection points?

The second derivative can be used to find inflection points, which are points on a curve where the concavity changes. This can be done by setting the second derivative equal to zero and solving for x. The x-values obtained are the potential inflection points, and further analysis can determine if they are actual inflection points.

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