Math Problem Statement

Find the volume of the solid formed by rotating the region bounded by the given curves y = -|x - 2| + 2, y = 0 about the y-axis.

Solution

To solve this problem, we need to compute the volume of the solid generated by rotating the region bounded by the given equations y=x2+2y = -|x - 2| + 2 and y=0y = 0 about the yy-axis.

Steps:

  1. Understand the Shape of the Region:

    • y=x2+2y = -|x - 2| + 2 represents a "V"-shaped graph with its vertex at (2,2)(2, 2), symmetric about x=2x = 2, decreasing linearly on both sides.
  2. Boundaries of Integration:

    • Since y=0y = 0 is the x-axis, the region is bounded between y=0y = 0 and y=x2+2y = -|x - 2| + 2.
    • Solve for xx in terms of yy: Split into two linear equations depending on xx: x=2y(left branch)andx=2+y(right branch).x = 2 - y \quad \text{(left branch)} \quad \text{and} \quad x = 2 + y \quad \text{(right branch)}.
  3. Volume via Shell Method:

    • The formula for the volume of a solid of revolution about the yy-axis using the shell method is: V=2πy=0y=2(radius)×(height)dy.V = 2\pi \int_{y=0}^{y=2} (\text{radius}) \times (\text{height}) \, dy.
    • The radius is yy, and the height is xrightxleft=(2+y)(2y)=2yx_{\text{right}} - x_{\text{left}} = (2 + y) - (2 - y) = 2y.
  4. Set up the Integral: V=2πy=0y=2y2ydy=4π02y2dy.V = 2\pi \int_{y=0}^{y=2} y \cdot 2y \, dy = 4\pi \int_{0}^{2} y^2 \, dy.

  5. Solve the Integral: y2dy=y33.\int y^2 \, dy = \frac{y^3}{3}. Apply the limits 00 to 22: 02y2dy=233033=83.\int_{0}^{2} y^2 \, dy = \frac{2^3}{3} - \frac{0^3}{3} = \frac{8}{3}.

  6. Compute the Volume: V=4π83=32π3.V = 4\pi \cdot \frac{8}{3} = \frac{32\pi}{3}.

  7. Numerical Approximation: Using π3.14159\pi \approx 3.14159: V323.14159333.51.V \approx \frac{32 \cdot 3.14159}{3} \approx 33.51.

Final Answer:

The volume of the solid is approximately 33.51 cubic units.

Let me know if you'd like further clarification or additional details. Here are some related questions:

  1. How is the shell method different from the disk/washer method?
  2. What happens if the solid is revolved about the xx-axis instead?
  3. Can this problem be solved using polar coordinates?
  4. How does the absolute value in the function affect the region's boundaries?
  5. What if the function was y=x+2y = -|x| + 2 instead? Would the volume change?

Tip: Always sketch the region and axis of revolution to visualize the problem better before setting up the integral.

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Math Problem Analysis

Mathematical Concepts

Calculus
Solid of Revolution
Integral Calculus

Formulas

Volume using Shell Method: V = 2π ∫ (radius) * (height) dy
Integral of y^2: ∫ y^2 dy = y^3 / 3

Theorems

Fundamental Theorem of Calculus

Suitable Grade Level

College Level