Consider the inexact differential form,  This must be inexact by considering going to the point . If we first increase  and then increase , then that corresponds to first integrating over  and then over . Integrating over  first contributes  and then integrating over  contributes . Thus, along the first path we get a value of 2. However, along the second path we get a value of . We can make  an exact differential by multiplying it by , yielding . And so  is an exact differential.