2. Using the notation: Y, for the outcome of person i, R; for the running variable, D; for the binary variable equal to one for treated observations (i.e., the R; passes the cutoff, ro). Write the regression equation corresponding with models that allow for: Page 2 (a) (5 points) a linear relationship between R; and Y, that allows for different in- tercepts for fitted values to the left and right of the cutoff (b) (5 points) a linear relationship between R; and Y, that allows for different in- tercepts and slopes for fitted values to the left and right of the cutoff (c) (5 points) a quadratic relationship between R; and Y, that allows for different intercepts, slopes, and quadratic terms for fitted values to the left and right of the cutoff