Consider the circle on the graph. Its center at the origin and its radius is 7. State the equation of the circle.

Please directly answer the question and provide the final value, e.g., 1, 2.5, 300.
Question: Consider the circle on the graph. Its center at the origin and its radius is 7. State the equation of the circle.

Please first conduct reasoning, and then answer the question and provide the final value, e.g., 1, 2.5, 300, at the end.
Question: Consider the circle on the graph. Its center at the origin and its radius is 7. State the equation of the circle.
