Write the equation for the piecewise function symmetric to x=3, which goes through (3,0) and (0, 3).

Please directly answer the question and provide the final value, e.g., 1, 2.5, 300.
Question: Write the equation for the piecewise function symmetric to x=3, which goes through (3,0) and (0, 3).

Please first conduct reasoning, and then answer the question and provide the final value, e.g., 1, 2.5, 300, at the end.
Question: Write the equation for the piecewise function symmetric to x=3, which goes through (3,0) and (0, 3).
