This is the solution provided by my teacher . I understand the math but I don't understand the logic.Pleaseexplainwhy did my teacher do it in terms of dxdy and how can i know when to do it in terms of dydx instead .please explain in detailslike by looking at the shapes of problems how do i know if it's in terms of dydx or dxdy. Is there a trick to it so I can understand how to do it faster?

8. Compute the following double integral ffm where R is the region conned between two parabolas x = y\