Chapter 7: Problem 92
Describe geometrically all points in 3-space whose coordinates satisfy the given condition(s). $$ x^{2}+y^{2}+(z-1)^{2}=4, z=2 $$
Short Answer
Expert verified
A circle with radius \( \sqrt{3} \) centered at \((0,0,2)\).
Step by step solution
01
Understand the First Equation
Consider the equation \( x^2 + y^2 + (z-1)^2 = 4 \). This is the equation of a sphere in three-dimensional space, centered at the point \((0, 0, 1)\) with a radius of 2.
02
Analyze the Second Condition
The condition \( z = 2 \) specifies a horizontal plane in three-dimensional space at the height where the z-coordinate is constantly 2.
03
Intersection of the Sphere and the Plane
To find the geometrical description of the points, consider where the plane \( z = 2 \) intersects with the sphere. Substitute \( z = 2 \) into the sphere's equation: \( x^2 + y^2 + (2-1)^2 = 4 \).
04
Simplify the Equation
Substituting \( z = 2 \) into the sphere equation transforms it into \( x^2 + y^2 + 1 = 4 \), which simplifies to \( x^2 + y^2 = 3 \).
05
Describe the Geometrical Shape
The equation \( x^2 + y^2 = 3 \) describes a circle in the xy-plane, centered at \((0, 0)\) with a radius of \( \sqrt{3} \), located at the height \( z = 2 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Sphere
A sphere is a perfectly symmetrical 3D shape where every point on its surface is an equal distance from its center. This distance is known as the radius.
- The equation for a sphere is typically: \( (x - h)^2 + (y - k)^2 + (z - l)^2 = r^2 \). Here, \(h, k, l\) are the coordinates of the center, and \(r\) is the radius.
- In the given exercise, the sphere is represented by \( x^2 + y^2 + (z - 1)^2 = 4 \). This tells us that the sphere's center is at \(0, 0, 1\) and its radius is 2.
Plane
A plane extends infinitely in two dimensions and is a flat, flat surface without edges. It's defined mathematically by a linear equation.
- The simplest plane, parallel to one of the coordinate planes, can take the form such as \( z = c \), where all points on the plane share the same z-coordinate.
- In the context of the exercise, the plane is described by \( z = 2 \), indicating a horizontal plane parallel to the xy-plane, located two units above the origin along the z-axis.
Intersection of Geometric Shapes
The intersection of two geometric shapes occurs where their equations simultaneously hold, producing common points or curves.
- When intersecting a plane and a sphere, you analyze how the flat infinite plane intersects the curved surface of the sphere.
- For the sphere \( x^2 + y^2 + (z-1)^2 = 4 \) and the plane \( z = 2 \), substituting \( z = 2 \) into the sphere's equation simplifies to \( x^2 + y^2 = 3 \), indicating a circular intersection.
Circle in Space
A circle in space represents a set of points equidistant from a central point within a plane.
- It can appear as the cross-section of a more complex shape, like when a plane cuts through a sphere.
- In the example given, the intersection formed where \( x^2 + y^2 = 3 \) describes a circle in the plane \( z = 2 \).
- This circle has its center at \(0, 0, 2\) and radius \( \sqrt{3} \), derived from simplifying the intersected sphere equation.