Revision as of 20:35, 18 September 2008 by Ctuchek (Talk)

Math 181 Honors Calculus

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Homework Help

Hello, this is gary from ma181. let's solve the extra credit problem. Here is the problem in italics:

Extra Credit Problem


Suppose that f(x) is continuously differentiable on the interval [a,b]. Let N be a positive integer and let $ M = Max { |f'(x)| : a \leq x \leq b } $. Let $ h = \frac{(b-a)}{N} $ and let $ R_N $ denote the "right endpoint" Riemann Sum for the integral $ I = \int_a^b f(x) dx . $ In other words, $ R_N = \sum_{n=1}^N f(a + n h) h . $

Explain why the error, $ E = | R_N - I | $, satisfies $ E < \frac{M(b-a)^2}{N}. $

  • So what does this equation "E < M(b-a)^2/N" mean. This reads that the error is less than the Maximum value of the derivative of the function of x multiplied by the interval squared from x=a to x=b all divided by the total number of subintervals N.
  • I don't understand why this must be true. Maybe I'm wrong, but if f(x) were a horizontal line, wouldn't E=0 and M(b-a)^2/N also be =0. That would mean it is a false statement that E < M(b-a)^2/N. Are we to assume that E <= M(b-a)^2/N?
  • Chumbert: Yeah, he said in class today (Wed.) to assume that, right?
  • Ctuchek - I do remember him saying that we will need to use the Mean Value Theorem.

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