There is a piecewise function combind by straight lines going through (3, -2), (1, 0), and (0,1). Write an equation for the graphed function f.

Please directly answer the question and provide the final value, e.g., 1, 2.5, 300.
Question: There is a piecewise function combind by straight lines going through (3, -2), (1, 0), and (0,1). Write an equation for the graphed function f.

Please first conduct reasoning, and then answer the question and provide the final value, e.g., 1, 2.5, 300, at the end.
Question: There is a piecewise function combind by straight lines going through (3, -2), (1, 0), and (0,1). Write an equation for the graphed function f.
