H O The center of a circle is at (-3, 1) and its radius is 9. What is the equation of the circle? O (x+3)² + (y-1)² = 81 O(x-3)² + (y + 1)² = 81 O (x+3)² + (y-1)² = 18 O(x-3)² + (y + 1)² = 18 3 4 $ 4 ER 5 T 6 & 7 1

Elementary Geometry For College Students, 7e
7th Edition
ISBN:9781337614085
Author:Alexander, Daniel C.; Koeberlein, Geralyn M.
Publisher:Alexander, Daniel C.; Koeberlein, Geralyn M.
ChapterP: Preliminary Concepts
SectionP.CT: Test
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### Circle Equation Determination

#### Problem Statement:
The center of a circle is at \((-3, 1)\) and its radius is 9.

**Question:**
What is the equation of the circle?

#### Options:
- \((x + 3)^2 + (y - 1)^2 = 81\)
- \((x - 3)^2 + (y + 1)^2 = 81\)
- \((x + 3)^2 + (y - 1)^2 = 18\)
- \((x - 3)^2 + (y + 1)^2 = 18\)

### Explanation:
In this problem, you are given the center \((h, k)\) of the circle and its radius \(r\). The standard form of the equation of a circle is:
\[
(x - h)^2 + (y - k)^2 = r^2
\]

Substituting \(h = -3\), \(k = 1\), and \(r = 9\):
\[
(x - (-3))^2 + (y - 1)^2 = 9^2
\]
\[
(x + 3)^2 + (y - 1)^2 = 81
\]

Therefore, the correct answer is:
- \((x + 3)^2 + (y - 1)^2 = 81\)
Transcribed Image Text:### Circle Equation Determination #### Problem Statement: The center of a circle is at \((-3, 1)\) and its radius is 9. **Question:** What is the equation of the circle? #### Options: - \((x + 3)^2 + (y - 1)^2 = 81\) - \((x - 3)^2 + (y + 1)^2 = 81\) - \((x + 3)^2 + (y - 1)^2 = 18\) - \((x - 3)^2 + (y + 1)^2 = 18\) ### Explanation: In this problem, you are given the center \((h, k)\) of the circle and its radius \(r\). The standard form of the equation of a circle is: \[ (x - h)^2 + (y - k)^2 = r^2 \] Substituting \(h = -3\), \(k = 1\), and \(r = 9\): \[ (x - (-3))^2 + (y - 1)^2 = 9^2 \] \[ (x + 3)^2 + (y - 1)^2 = 81 \] Therefore, the correct answer is: - \((x + 3)^2 + (y - 1)^2 = 81\)
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