2. Consider a Keynesian IS-LM model for national income: IS: Y =C(Y -T) +I(r) +G LM: L(r, Y) = M* where we consider Y and r as the endogenous variables and G, MS, and T as the exogenous variables. (a) Find the effect of a lump-sum tax, T, change on Y, i.e., OY/OT, using the implicit function theorem