Finding the solution To answer this question, we first substitute(1)and (2)into the equilibrium condition ( 3). The result is the following differential equation dt s pl or i dt ps (4) Since(4)specifies a definite pattern of change for 1, we should be able to find the equilibrium (or required)investment path from it In this simple case, the solution is obtainable by directly integrating both sides of the second equation in(4) with respect to t. The fact that the two sides are identical in equilibrium assures the equality of their integrals. ThusFinding the Solution To answer this question, we first substitute (1) and (2) into the equilibrium condition (3). The result is the following differential equation: I dt s dI =  1 or s dt dI I =  1 ( 4 ) Since (4) specifies a definite pattern of change for I, we should be able to find the equilibrium (or required) investment path from it. In this simple case, the solution is obtainable by directly integrating both sides of the second equation in (4) with respect to t. The fact that the two sides are identical in equilibrium assures the equality of their integrals. Thus