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

In summary, the conversation discusses methods of approximating the area under a curve, specifically using trapezoids and rectangles with left endpoints. It is noted that the value obtained using n trapezoids is equal to the average of the values obtained using rectangles with left and right endpoints. Additionally, it is mentioned that if f'' > 0 and f is increasing on [a, b], then the midpoint method will always underestimate the area under the curve.
  • #1
chjopl
21
0
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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  • #2
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.
 
  • #3
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.
 

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

1. What is trapezoid integration?

Trapezoid integration, also known as the trapezoidal rule, is a numerical method used for approximating the definite integral of a function. It involves dividing the interval of integration into smaller trapezoids and calculating the area under each trapezoid to estimate the total area under the curve.

2. How does trapezoid integration work?

Trapezoid integration works by using the formula: ∫f(x) dx ≈ (b-a) * [(f(a) + f(b))/2], where a and b are the limits of integration and f(x) is the function being integrated. This formula calculates the area of a trapezoid by taking the average of the function's values at the two endpoints of the interval and multiplying it by the width of the interval.

3. What are the advantages of using trapezoid integration?

Trapezoid integration is a simple and easy-to-use method for approximating integrals. It also provides a more accurate estimate compared to other basic numerical methods, such as the midpoint rule. Additionally, it can be used to approximate the integral of non-smooth functions that may not be easily integrated analytically.

4. What are the limitations of trapezoid integration?

One limitation of trapezoid integration is that it can only provide an approximation of the integral, not the exact value. Also, the accuracy of the approximation depends on the number of trapezoids used, so a large number of trapezoids may be needed for complex functions. Additionally, trapezoid integration may not work well for functions with sharp peaks or discontinuities.

5. How is trapezoid integration used in real-life applications?

Trapezoid integration is commonly used in fields such as physics, engineering, and economics to approximate the area under curves and solve problems that involve integrals. It is also used in computer programming for numerical integration and in statistics for approximating probabilities.

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