Finding Center and Radius of a Sphere

In summary, the problem is asking for the set of all points that are twice as far from the point A (-1,5,3) as they are from the point B (6,2,-2). This set forms a sphere with center (2.5, 3.5, 0.5) and radius \sqrt{83}. To find |PA| and |PB|, use the distance formula and set |PA| = 2|PB|, then simplify to get the desired result.
  • #1
mujadeo
103
0

Homework Statement


If distance |AB| = root 83, and i also know that |PA| is twice |PB|, then how do you find? |PA| or |PB| ?

The whole question states: consider the points P such that the distance from P to A (-1,5,3) is twice the distance from P to B (6,2,-2).
Show that the set of all such points is a sphere, and find its center and radius.
please help!



Homework Equations





The Attempt at a Solution

 
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  • #2
Let P=(x,y,z) and then the vector PB would be (6-x,2-y,-2-z)
Similarly, do with A...then use the fact that |PA|=2|PB|
 
  • #3
Do you know the distance formula? Let P be the general point (x,y,z). Then the distance from P to (-1, 5, 3) is [itex]\sqrt{(x+1)^2+ (y-5)^2+ (z-3)^2}[/itex] and the distance from P to (6, 2, -2) is [itex]\sqrt{(x- 6)^2+ (y-2)^2+ (z+2)^3}[/itex]. Those are the |PA| and |PB| rock.freak667 is talking about. Put them into the equation he gives and simplify (I would square both sides).
 

1. How do you find the center of a sphere?

The center of a sphere is the point that is equidistant from all points on the surface of the sphere. To find the center, you can take the average of the x, y, and z coordinates of any three non-collinear points on the sphere.

2. What is the equation for finding the radius of a sphere?

The equation for finding the radius of a sphere is r = √(x0² + y0² + z0²), where (x0, y0, z0) is the center point of the sphere.

3. Can the radius of a sphere be negative?

No, the radius of a sphere cannot be negative. It is a measure of distance and distance cannot be negative.

4. How does the center and radius of a sphere affect its volume and surface area?

The center and radius of a sphere are directly related to its volume and surface area. The volume of a sphere is calculated using the equation V = (4/3)πr³, where r is the radius. The surface area of a sphere is calculated using the equation A = 4πr². As the radius increases, both the volume and surface area of the sphere will increase.

5. How can I use the center and radius of a sphere in real-world applications?

The center and radius of a sphere can be used in various real-world applications, such as calculating the volume and surface area of a water tank, determining the distance between two objects in space, or creating 3D models for video games or simulations. It is also essential in geometry and physics when studying shapes and forces in three-dimensional space.

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