Differential Equations--Finding Constants 1. The problem statement, all variables and given/known data I uploaded a pdf document, which contains the problem I am currently working on, namely, problem number 7 2. Relevant equations 3. The attempt at a solution I am having particular difficulty with this portion of the solution: "(ii) At y=3, the function ay+b changes from positive to negative --> ay+b has a negative slope --> a is negative" Why does "a" being negative follow from these facts? Also, why does a function change signs at y = 3?