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Give a geometric description of the following set of points. \( x^{2}-12 x+y^{2}+z^{2} \geq-20 \) Choose the correct answer below. A. The exterior of a ball with center \( (6,0,0) \) and radius 4 (including the sphere itself) B. A ball with center \( (-6,0,0) \) and radius 4 C. A ball with center \( (6,0,0) \) and radius 4 D. The exterior of a ball with center \( (-6,0,0) \) and radius 4 (including the sphere itself) E. The entire xyz-coordinate system F. The empty xyz-coordinate system

Ask by Christensen Schofield. in the United States
Jan 22,2025

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Tutor-Verified Answer

Answer

The set of points is the exterior of a ball centered at \( (6,0,0) \) with a radius of 4, including the sphere itself.

Solution

To describe the set of points defined by the inequality: \[ x^{2} - 12x + y^{2} + z^{2} \geq -20, \] let's rewrite the expression by completing the square for the \( x \)-term: 1. **Complete the Square for \( x \):** \[ x^{2} - 12x = (x - 6)^2 - 36. \] 2. **Substitute Back into the Inequality:** \[ (x - 6)^2 - 36 + y^{2} + z^{2} \geq -20. \] 3. **Rearrange the Inequality:** \[ (x - 6)^2 + y^{2} + z^{2} \geq -20 + 36, \] \[ (x - 6)^2 + y^{2} + z^{2} \geq 16. \] This inequality represents all points \((x, y, z)\) in three-dimensional space whose distance from the center \((6, 0, 0)\) is **at least 4**, since \( \sqrt{16} = 4 \). **Geometrically**, this describes the **exterior** of a sphere (or ball) centered at \((6, 0, 0)\) with a radius of 4. The inequality includes the surface of the sphere itself. **Correct Answer:** A. The exterior of a ball with center \( (6,0,0) \) and radius 4 (including the sphere itself)

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Mind Expander

To analyze the inequality \( x^{2}-12 x+y^{2}+z^{2} \geq-20 \), we first rearrange the equation. Completing the square for the \( x \) terms gives: \[ (x-6)^{2} - 36 + y^{2} + z^{2} \geq -20 \] This simplifies to: \[ (x-6)^{2} + y^{2} + z^{2} \geq 16 \] The right side can be expressed as \( 4^2 \), which indicates a relationship to a sphere. This inequality describes the exterior of a sphere (including its surface) centered at \( (6, 0, 0) \) with a radius of 4. Therefore, the correct answer is: **A. The exterior of a ball with center \( (6,0,0) \) and radius 4 (including the sphere itself)**. Now for a little bit more insight: In mathematical terms, the inequality illustrates points that are at a distance greater than or equal to 4 units from the point (6, 0, 0). This means any point within that distance (inside the ball) does not satisfy the inequality, leading to a fun visual of the space outside of that spherical ball while allowing the surface itself! If you enjoy geometry, visualizing 3D shapes can be quite fun! Imagine blowing up a balloon from the center point (6, 0, 0) outwards; all those points on the balloon and outside are included in this set. It’s a fantastic way to see mathematics in action!

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