Reducible to exact differential equations 4 steps and where to use them?

see attached , if convert the differential equations into exact form then it's solutions can be found using this formula directly , that's why we convert into exact..

To solve exact Differential equations.

we use this method for simplicity for time save to determine the equation is exact or not here the steps in image any doubt, plz ask, we will discuss i will also sent pdf of iit m...