Math Problem Statement

Let [R] be the region enclosed by the line [x=-4], the line [y=1], the line [y=4], and the curve [y=e^x]. Line x = negative 4 and curve y = e to the x power are graphed. The curve moves along the negative x axis, then moves upward with increasing steepness. It intersects the line at (negative 4, 0), then moves upward to the right of it. The area enclosed by the two plots between y = 1 and y = 4 is shaded, representing region R. [y] [x] [\blueD{y=e^x}] [\small -4] [\large R] [\small 1] [\small 4] A solid is generated by rotating [R] about the line [x=-4]. Which one of the definite integrals gives the volume of the solid? Choose 1 answer: Choose 1 answer:

Solution

To find the volume of the solid generated by rotating the region RR around the line x=4x = -4, we need to set up the integral using the method of cylindrical shells.

Step 1: Determine the formula for the volume using cylindrical shells

The formula for the volume using cylindrical shells when rotating around a vertical line (like x=4x = -4) is given by:

V=2πyminymax(radius)×(height)dyV = 2\pi \int_{y_{\text{min}}}^{y_{\text{max}}} \text{(radius)} \times \text{(height)} \, dy

Step 2: Identify the radius and height

  • Radius: The distance from the axis of rotation x=4x = -4 to a point on the curve is given by the horizontal distance between x=4x = -4 and xx on the curve. Thus, the radius r(y)=x+4=lny+4=lny+4r(y) = |x + 4| = | \ln y + 4 | = \ln y + 4.

  • Height: The height of the shell is the difference between the yy-values, which is yy (since we are using yy as the independent variable in this approach).

Step 3: Determine the limits of integration

The region RR is enclosed between y=1y = 1 and y=4y = 4, so the limits of integration are from y=1y = 1 to y=4y = 4.

Step 4: Set up the integral

Thus, the volume of the solid is:

V=2π14(lny+4)ydyV = 2\pi \int_{1}^{4} (\ln y + 4) \cdot y \, dy

However, the problem asks which of the definite integrals corresponds to the correct setup. The integral expression that matches the setup described above would be the following:

V=2π14(lny+4)ydyV = 2\pi \int_{1}^{4} (\ln y + 4) \cdot y \, dy

This represents the correct definite integral to calculate the volume of the solid generated by rotating the region RR about the line x=4x = -4.

Would you like more details on this solution, or do you have any questions?


Relative Questions:

  1. How would the integral change if the rotation were around y=0y = 0 instead?
  2. What is the significance of the height function in the method of cylindrical shells?
  3. How would you set up the integral if the region RR was rotated around the y-axis instead of x=4x = -4?
  4. Can the disk/washer method be applied to this problem? If yes, how?
  5. What if the curve y=exy = e^x was replaced with y=x2y = x^2; how would the integral change?

Tip: Always visualize the region and the axis of rotation to help determine the correct method and setup for the integral.

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Math Problem Analysis

Mathematical Concepts

Calculus
Integral Calculus
Volume of Revolution
Cylindrical Shells Method

Formulas

Volume using cylindrical shells: V = 2\pi \int_{y_{\text{min}}}^{y_{\text{max}}} (\text{radius}) \cdot (\text{height}) \, dy

Theorems

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Suitable Grade Level

Advanced High School