Chapter 13: Problem 5
The part of the cylinder \(x^{2}+z^{2}=9\) that is directly over the rectangle in the \(x y\)-plane with vertices \((0,0),(2,0),(2,3)\), and \((0,3)\)
Short Answer
Expert verified
The solution is a cylindrical surface segment over the rectangle with x-values from 0 to 2, y-values from 0 to 3, and z-values based on the equation \(z^2 = 9 - x^2\).
Step by step solution
01
Understanding the Problem
We are given a cylinder with the equation \(x^{2}+z^{2}=9\). This equation describes a cylinder along the y-axis with a radius of 3, since replacing \(x\) and \(z\) gives a circle with radius 3 when sliced by any plane parallel to the xy-plane. We need to find the part of this cylinder that lies directly above a rectangle in the xy-plane with vertices \((0,0), (2,0), (2,3), (0,3)\).
02
Defining the Bounds for x and y
The rectangle in the xy-plane defines the domain for \(x\) and \(y\). The bounds for \(x\) are from 0 to 2, and for \(y\), from 0 to 3.
03
Analyzing Cylinder Constraints
The cylinder's surface is defined by the equation \(x^{2} + z^{2} = 9\). Since \(x\) can range from 0 to 2, substituting it into the cylinder's equation gives possible values for \(z\). For these x-values, \(z\) will vary within \([-\sqrt{9-x^2}, \sqrt{9-x^2}]\).
04
Constructing the Solid
Since \(y\) reflects the depth/direction along the axis of the cylinder, \(z\) is determined only by \(x\) due to the cylinder's equation. The valid z-values for each \(x\) are described by the cylinder's equation. Therefore, for each fixed \(x\) in the interval \([0, 2]\), the \(z\)-coordinate can be anywhere between \(-\sqrt{9-x^2}\) and \(\sqrt{9-x^2}\), and \(y\) can vary from 0 to 3.
05
Calculating the Limits of z When x=0 and x=2
For \(x=0\), \(z^2=9\), thus \(z = \pm 3\). For \(x=2\), \(z^2=5\), thus \(z = \pm \sqrt{5}\). The function \(z=\sqrt{9-x^2}\) decreases from 3 to \(\sqrt{5}\) as \(x\) goes from 0 to 2, defining the top half of the cylinder over the rectangle.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Cylinder Equation
The cylinder equation given is \(x^2 + z^2 = 9\). This equation represents a 3D surface in space. A cylinder can be thought of as a series of circles stacked along a line—in this case, the y-axis. When we see an equation in the form \(x^2 + z^2 = R^2\), it's describing a cylinder with a radius \(R\) along the third variable's axis—here, the y-axis.
The equation can be visualized as:
The equation can be visualized as:
- Each slice parallel to the top circle (the xy-plane) is a circle with radius 3 at any point along the y-axis.
- The coordinates \((x, z)\) fit into a circle centered at the origin with given radius.
Limits of Integration
When tackling any 3D problem involving integration, defining the limits of integration is crucial. In this scenario, we're examining a part of the cylindrical surface directly above a rectangle in the xy-plane. The limits here define the 'area of interest.'
- The x-value ranges from 0 to 2, based on the rectangle's vertices projections onto the x-axis.
- For y-values, the range is from 0 to 3.
- The z-values are determined by the cylinder's restriction: they fluctuate from \(-\sqrt{9-x^2}\) to \(\sqrt{9-x^2}\).
Cylinder Radius
The radius of the cylinder is a fundamental property. This cylinder, defined by \(x^2 + z^2 = 9\), indicates a radius \(R = 3\). Understanding how the radius influences the cylinder is key.
- The radius determines the size of the circular cross-sections in the xz-plane.
- Any circle derived within the cylinder, parallel to xz, will always have this radius.
XYZ-Coordinate System
The xyz-coordinate system is foundational in visualizing problems involving three dimensions, like this cylinder over a rectangle.
- The x-axis runs horizontally, typically left to right.
- The y-axis runs vertically across the plane, often bottom to top.
- The z-axis comes towards or away from the viewer, providing depth.