Homer made an error in step 2
When completing the square, it's necessary to apply the adjustments to both sides of the equation
Solution:
The provided equation for the circle:

First, let’s determine the center and the radius and identify where the mistake occurred
Step 1:
Group the terms

Step 2:

However, Homer’s second step is:

Thus, Homer committed an error during this step
When completing the square, the values must be added to both sides of the equation
However, Homer neglected to add 49 and 1 to the right side of the equation
Correct steps are:

By comparing with the general equation of a circle,

It follows that the center coordinates are ( 7, -1) and the radius measures 8.66