Let's break down the question step by step to guide you through solving it.

1. Integral to Approximate:

The integral you are asked to approximate is:

$\int_3^7 x^2 \sqrt{x^3 + 2} \, dx$

2. Approximation using Rectangles:

You need to approximate this integral using:

• Four rectangles
• Eight rectangles

And for each case:

• Left-endpoints
• Right-endpoints
• Midpoints

These approximations are typically part of Riemann sum methods:

• Left endpoint approximation uses the value of the function at the left side of each subinterval.
• Right endpoint approximation uses the function value at the right side.
• Midpoint approximation uses the value of the function at the midpoint of each subinterval.

3. Exact Value of the Integral:

After the approximations, you are required to compute the exact value of the integral either analytically (if possible) or using a calculator/numerical integration method. You will then compare the approximated values to the exact value.

4. Approximation Error:

Calculate the approximation error for each method using the formula:

$\text{Error} = |\text{Exact value} - \text{Approximation value}|$

5. Theoretical Discussion:

You are also asked to discuss whether it is possible, in principle, to find functions $f(x)$ for which the estimated integral is exactly equal to the actual value of the integral. This generally involves analyzing functions that are linear or constant, where the approximation methods like Riemann sums are exact.

Plan:

1. Step 1: Subdivide the interval $[3,7]$:

   • For 4 rectangles: Divide into intervals of width $\Delta x = 1$.
   • For 8 rectangles: Divide into intervals of width $\Delta x = 0.5$.

2. Step 2: Approximate using the left, right, and midpoint methods.

   • Compute function values at relevant points.
   • Multiply by the width $\Delta x$ and sum for each approximation.

3. Step 3: Find the exact value of the integral using numerical methods (such as a calculator or symbolic computation software).

4. Step 4: Calculate the approximation errors.

5. Step 5: Discuss the possibility of finding functions for which approximations match the exact integral value. Functions that are linear or constant are often exact for certain methods.

Would you like to proceed with the numerical calculations for each of the approximations, or do you need further clarification on any part of the problem?

Here are 5 questions to help explore this concept further:

1. How do you divide the interval $[3, 7]$ when using 4 or 8 rectangles for approximation?
2. What is the difference between left, right, and midpoint Riemann sums in practice?
3. Why does the midpoint approximation often give a better result than left or right endpoint approximations?
4. Can you think of any types of functions where the midpoint, left, and right approximations give the same result?
5. What types of functions have exact integrals when approximated using Riemann sums?

Tip: Midpoint approximation generally provides a more accurate estimate compared to left or right Riemann sums.