� A differential equation of the form 
+P
Q
dy
y
dx
, where P and Q are  constants
or functions of x only  is called a first order linear differential equation Historical Note
One of the principal languages of Science is that of differential equations Interestingly, the date of birth of differential equations is taken to be November,
11,1675, when Gottfried Wilthelm Freiherr Leibnitz (1646 - 1716) first put in black
and white the identity 
212
y dy
y
=
∫
, thereby introducing both the symbols ∫ and dy © NCERT
not to be republished
DIFFERENTIAL EQUATIONS
423
Leibnitz was actually interested in the problem of finding a curve whose tangents
were prescribed