Answer:
Step-by-step explanation:
A circle centered at (0,0) with radius r is
Since your circle has diameter of 12, then its radius is 6. Then
So a possible answer is:
If you want to move the location of the center, but keep it on the x-axis, then add or subtract a number to the x, such as this:
The center of this circle would be (-4, 0) which is still on the x-axis.