Is Mid(n) an Underestimate for Trapezoid Integration on an Increasing Function?

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SUMMARY

The discussion centers on the trapezoidal rule for numerical integration, specifically examining whether the midpoint approximation, Mid(n), underestimates the integral of an increasing function. It is established that TRAP(n) represents the area approximation using n trapezoids, and that Left(n) refers to the left endpoint approximation. The relationship TRAP(n) = (Left(n) + Right(n)) / 2 is confirmed, highlighting that the only differences in Left(n) and Right(n) occur at the endpoints. The conclusion asserts that for a function f where f'' > 0 and f is increasing on the interval [a, b], Mid(n) is definitively an underestimate of the integral of f(x) dx from a to b.

PREREQUISITES
  • Understanding of numerical integration techniques, specifically the trapezoidal rule.
  • Familiarity with concepts of left and right endpoint approximations in integration.
  • Knowledge of calculus, particularly the implications of second derivatives on function behavior.
  • Basic understanding of increasing functions and their properties.
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  • Study the derivation and application of the trapezoidal rule in numerical integration.
  • Learn about the properties of increasing functions and their implications for integration.
  • Explore the relationship between the second derivative and concavity in functions.
  • Investigate other numerical integration methods, such as Simpson's Rule, for comparison.
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Mathematicians, students studying calculus, and professionals involved in numerical analysis or computational mathematics will benefit from this discussion.

chjopl
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For F(x) dx from a to b show TRAP(n)=Left(n) + 1/2 (f(b)-f(a))*delta x
 
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I assume that TRAP(n) is the value you would get using n trapezoids to approximate the area. Is Left(n) the approximation using rectangles with height the left endpoint?

If so, you might note that TRAP(n)= (Left(n)+ Right(n))/2 and that the sums involved in Left(n) and Right(n) differ only at the two endpoints.
 
Thanks for the help but now i have another problem
Let f''> 0 and suppose f is increasing on [a,b], show that Mid(n) is an underestimate for f(x) dx from a to b.
 

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