Chapter 11: Problem 12
Find the equation of the sphere whose center is \((2,4,5)\) and that is tangent to the \(x y\) -plane.
Short Answer
Expert verified
The sphere's equation is \((x - 2)^2 + (y - 4)^2 + (z - 5)^2 = 25\).
Step by step solution
01
Understand the Tangent Condition
The sphere being tangent to the \(xy\)-plane means that the distance from the center of the sphere \((2,4,5)\) to the \(xy\)-plane is equal to the radius. The \(xy\)-plane can be described by the equation \(z = 0\). Therefore, the radius is simply the \(z\)-coordinate of the center, which is 5.
02
Apply the Sphere Equation Formula
The general equation of a sphere with center \((h, k, l)\) and radius \(r\) is: \((x - h)^2 + (y - k)^2 + (z - l)^2 = r^2\). Substituting the given center \((2,4,5)\) and radius \(5\), the equation becomes: \((x - 2)^2 + (y - 4)^2 + (z - 5)^2 = 5^2\).
03
Simplify the Equation
Simplify the equation obtained in the previous step: \((x - 2)^2 + (y - 4)^2 + (z - 5)^2 = 25\). This is the final equation of the sphere.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Tangent Condition
When discussing spheres, the tangent condition refers to a situation where a sphere just touches a plane. This point of contact is called tangency. In this exercise, the sphere is tangent to the \(xy\)-plane. The \(xy\)-plane is represented by the equation \(z = 0\).
- The sphere's center is at \((2,4,5)\).
- Tangency means the distance from the center of the sphere to the plane is exactly the radius.
Sphere Center
The center of a sphere is the fixed point from which every point on the sphere's surface is equidistant. It's a crucial part of the sphere's equation. In our problem, the center is at \((2, 4, 5)\). This location includes specific coordinates:
- \(x\)-coordinate: 2
- \(y\)-coordinate: 4
- \(z\)-coordinate: 5
Radius
The radius is the distance from the center of the sphere to any point on its surface. It's a key element to describe the size of the sphere. In our problem, because the sphere is tangent to the \(xy\)-plane, the radius is precisely the \(z\)-coordinate of the center which is 5.
Here’s why:
Here’s why:
- The distance from the center at \((2, 4, 5)\) to the \(xy\)-plane \(z = 0\) is 5.
- That same distance acts as the radius due to the tangent condition.
3D Coordinates
3D coordinates consist of three values \((x, y, z)\), representing a point in three-dimensional space. For a sphere, these coordinates explain location and orientation:
- The \(x\)-coordinate shows left-right positioning.
- The \(y\)-coordinate explains forward-backward movement.
- The \(z\)-coordinate describes up-down altitude.