Answer:

Explanation:
The standard equation of a circle with center (h, k) and radius (r) is:

Given that the center of the circle is the origin (0, 0):
Therefore, the standard equation of a circle where its center is at the origin is:

The radius of a circle is half its diameter.
Given the diameter of the circle is 24 units, then its radius is:
So, the standard equation of a circle that has its center at the origin and a diameter of 24 units is:
