Math Problem Statement

Estimate the area under the graph of f(x) = 5/x between x = 1 and x = 17 using the midpoint rule with two rectangles and four rectangles.

Solution

To estimate the area under the graph of f(x)=5xf(x) = \frac{5}{x} between x=1x = 1 and x=17x = 17 using the midpoint rule, we will calculate it with:

  1. Two rectangles.
  2. Four rectangles.

Step 1: Using Two Rectangles

  • The interval length is 171=1617 - 1 = 16.
  • Divide the interval into two subintervals: [1,9][1, 9] and [9,17][9, 17].
  • Width of each rectangle: Δx=162=8\Delta x = \frac{16}{2} = 8.
  • Midpoints of the subintervals:
    • For [1,9][1, 9]: Midpoint = 1+92=5\frac{1 + 9}{2} = 5.
    • For [9,17][9, 17]: Midpoint = 9+172=13\frac{9 + 17}{2} = 13.

Now calculate the height of the rectangles using f(x)f(x) at these midpoints:

  • f(5)=55=1f(5) = \frac{5}{5} = 1.
  • f(13)=5130.3846f(13) = \frac{5}{13} \approx 0.3846.

Area estimate: Area=Δx[f(5)+f(13)]=8(1+0.3846)81.3846=11.0768.\text{Area} = \Delta x \cdot \left[ f(5) + f(13) \right] = 8 \cdot (1 + 0.3846) \approx 8 \cdot 1.3846 = 11.0768.


Step 2: Using Four Rectangles

  • Divide the interval into four subintervals: [1,5][1, 5], [5,9][5, 9], [9,13][9, 13], [13,17][13, 17].
  • Width of each rectangle: Δx=164=4\Delta x = \frac{16}{4} = 4.
  • Midpoints of the subintervals:
    • For [1,5][1, 5]: Midpoint = 1+52=3\frac{1 + 5}{2} = 3.
    • For [5,9][5, 9]: Midpoint = 5+92=7\frac{5 + 9}{2} = 7.
    • For [9,13][9, 13]: Midpoint = 9+132=11\frac{9 + 13}{2} = 11.
    • For [13,17][13, 17]: Midpoint = 13+172=15\frac{13 + 17}{2} = 15.

Now calculate the height of the rectangles using f(x)f(x) at these midpoints:

  • f(3)=531.6667f(3) = \frac{5}{3} \approx 1.6667.
  • f(7)=570.7143f(7) = \frac{5}{7} \approx 0.7143.
  • f(11)=5110.4545f(11) = \frac{5}{11} \approx 0.4545.
  • f(15)=5150.3333f(15) = \frac{5}{15} \approx 0.3333.

Area estimate:

= 4 \cdot (1.6667 + 0.7143 + 0.4545 + 0.3333) \approx 4 \cdot 3.1688 = 12.6752.$$ --- ### **Final Estimates** - Using **two rectangles**: Approximate area = $$11.0768$$. - Using **four rectangles**: Approximate area = $$12.6752$$. Would you like further explanations, visualizations, or refinements for these calculations? --- ### **Five Questions for Expansion** 1. How does increasing the number of rectangles improve the approximation? 2. What is the exact value of the integral $$\int_{1}^{17} \frac{5}{x} \, dx$$ for comparison? 3. Can you generalize the midpoint rule for $$n$$ rectangles? 4. How does this method compare to other numerical integration techniques (e.g., trapezoidal rule)? 5. Why is the midpoint rule more accurate than using left or right endpoints? ### **Tip**: The midpoint rule generally yields more accurate results because it reduces the error caused by the curvature of the function.

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Math Problem Analysis

Mathematical Concepts

Numerical Integration
Midpoint Rule
Area Under Curve

Formulas

Midpoint Rule: Area = Δx * (f(midpoint1) + f(midpoint2) + ... + f(midpointn))

Theorems

Midpoint Rule for Numerical Integration

Suitable Grade Level

Grades 11-12