The room we are in is for various stuff when somebody needs to communicate with me. Or when I want to make a note about something or need to communicate with someone else.
now the book converts this equation into a linear differential equation, using the differential operator, now my book convert this equation into linear differential equation
I am not sure whether I follow.
Did you perhaps mean to say that it is converted to system of two differential equations?
For the benefit of others who are visiting room (or reading the transcript), I'll add that the above question about ODEs is now posted on the main site: Question related to differential operator.