Geometry

Question Analysis

The main focus is to determine the radius of the circle from the given equation . We need to transform the equation into the standard form of a circle equation to identify the radius.

 

Key Concept Explanation

The standard form of a circle's equation is , where  is the center of the circle and  is the radius. When the equation is in the form , we can rewrite it to the standard form to find  by isolating  and comparing with .

 

Step-by-Step Solution

1. Given the equation .

2. Add 81 to both sides of the equation to get it in the form .

3. Compare

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