e ,
g (x, y, y′, a) = 0 (2)
The required differential equation is then obtained by eliminating a from equations
(1) and (2) as
F(x, y, y′) = 0 (3)
(b)
If the given family F2 of curves depends on the parameters a, b (say) then it is
represented by an equation of the from
F2 (x, y, a, b) = 0