Proving the Second Derivative Using L'Hopital's Rule

In summary, to show that lim(h-->0) [f(x+h)-2f(x) + f(x-h)]/h^2 is equal to f''(x) for any given value of x where the second derivative exists, you can use L'Hopital's rule and rewrite the expression as the average of the left and right limits for the derivative of f(x), assuming that f is differentiable in an entire neighborhood of x.
  • #1
barksdalemc
55
0

Homework Statement



Show that lim(h-->0) [f(x+h)-2f(x) + f(x-h)]/h^2
is equal to f''(x) for any given value of x where the second derivative exists.


I'm supposed to use L'Hopitals rule for this problem. I did and got
[f(x+h)-f(x-h)]/2h

Now I am stuck. I thought about adding and subtracting say f(x) but don't see how that solves to f''(x)
 
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  • #2
You're almost there. You can rewrite that as the average of the left and right limits for the derivative of f(x), which will be the same if f is differentiable at x.
 
  • #3
f(x+h)-f(x-h)

is not the derivative of

f(x+h)-2f(x) + f(x-h)


p.s.: for the record, you have to assume f is differentiable in an entire neighborhood of x in order to invoke L'Hôpital's rule.
 
Last edited:

1. What is a second derivative?

A second derivative is a mathematical concept that describes the rate of change of a rate of change. It is the derivative of the derivative of a function.

2. Why is the second derivative important?

The second derivative is important because it helps us understand the shape and behavior of a function. It can tell us whether a function is increasing or decreasing, and whether it is concave up or concave down.

3. How is the second derivative calculated?

The second derivative is calculated by taking the derivative of the first derivative. This can be done using the power rule, product rule, quotient rule, or chain rule, depending on the function.

4. What is the difference between a first and second derivative?

The first derivative tells us the rate of change of a function, while the second derivative tells us the rate of change of the rate of change. In other words, the first derivative describes the slope of a function, while the second derivative describes the curvature of a function.

5. How can the second derivative be used in real-world applications?

The second derivative can be used in various fields such as physics, economics, and engineering to analyze and predict the behavior of systems. For example, in physics, the second derivative of an object's position with respect to time can tell us about its acceleration. In economics, the second derivative of a production function can help determine the optimal level of production.

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