Math Problem Statement

Consider the solid that lies above the square (in the xy-plane) R = [0, 2] × [0, 2], and below the elliptic paraboloid z = 64 − x^2 − 3y^2. Using iterated integrals, compute the exact value of the volume.

Solution

The problem asks to compute the volume of the solid bounded above by the elliptic paraboloid z=64x23y2z = 64 - x^2 - 3y^2 and the square region R=[0,2]×[0,2]R = [0, 2] \times [0, 2] in the xyxy-plane.

Solution Approach:

To find the volume of the solid, we will set up a double integral. The volume of the solid is given by:

V=Rz(x,y)dAV = \int\int_R z(x,y) \, dA where z(x,y)=64x23y2z(x,y) = 64 - x^2 - 3y^2 and R=[0,2]×[0,2]R = [0, 2] \times [0, 2].

So, the volume integral becomes: V=0202(64x23y2)dxdyV = \int_0^2 \int_0^2 (64 - x^2 - 3y^2) \, dx \, dy

Step-by-step Calculation:

  1. Integrate with respect to xx:

02(64x23y2)dx=02(643y2)dx02x2dx\int_0^2 (64 - x^2 - 3y^2) \, dx = \int_0^2 (64 - 3y^2) \, dx - \int_0^2 x^2 \, dx

The first part: 02(643y2)dx=(643y2)x02=(643y2)2=1286y2\int_0^2 (64 - 3y^2) \, dx = (64 - 3y^2) \cdot x \Big|_0^2 = (64 - 3y^2) \cdot 2 = 128 - 6y^2

The second part: 02x2dx=x3302=83\int_0^2 x^2 \, dx = \frac{x^3}{3} \Big|_0^2 = \frac{8}{3}

So, the integral with respect to xx is: 1286y283128 - 6y^2 - \frac{8}{3} Simplifying: 3843836y2=37636y2\frac{384}{3} - \frac{8}{3} - 6y^2 = \frac{376}{3} - 6y^2

  1. Integrate with respect to yy:

Now, we need to integrate with respect to yy:

02(37636y2)dy\int_0^2 \left( \frac{376}{3} - 6y^2 \right) \, dy

First part: 023763dy=3763y02=37632=7523\int_0^2 \frac{376}{3} \, dy = \frac{376}{3} \cdot y \Big|_0^2 = \frac{376}{3} \cdot 2 = \frac{752}{3}

Second part: 026y2dy=6y3302=683=16\int_0^2 6y^2 \, dy = 6 \cdot \frac{y^3}{3} \Big|_0^2 = 6 \cdot \frac{8}{3} = 16

So, the total volume is: 752316=7523483=7043\frac{752}{3} - 16 = \frac{752}{3} - \frac{48}{3} = \frac{704}{3}

Thus, the exact volume is: 7043\boxed{\frac{704}{3}}


Would you like more details on any of the steps? Here are five related questions that might help expand your understanding:

  1. How would the volume change if the region RR were different?
  2. What happens to the volume if the equation of the paraboloid changes?
  3. Can you set up the integral in polar coordinates instead of Cartesian?
  4. How would the limits of integration change if the region RR were a different shape?
  5. What if the paraboloid intersected the xyxy-plane at different points?

Tip: When solving double integrals, breaking them into smaller integrals often simplifies the problem.

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Math Problem Analysis

Mathematical Concepts

Calculus
Double Integrals
Volume Calculation

Formulas

V = ∫∫_R z(x, y) dA
Iterated integral setup: V = ∫_0^2 ∫_0^2 (64 - x^2 - 3y^2) dx dy

Theorems

Fundamental Theorem of Calculus
Fubini's Theorem

Suitable Grade Level

Undergraduate Calculus