® A differential equation of the form +P , 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, , , when Gottfried Wilthelm Freiherr Leibnitz ( - ) first put in black and white the identity y dy , thereby introducing both the symbols ∫ and dy . 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 ’ . A year later he formulated the ‘ method of solving the homogeneous