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