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 This led him to discover the ‘method of separation of variables’
1691 A year later he formulated the ‘method of solving the homogeneous
differential equations of the first order’