Question
Form the differential equation of the family of parabolas having vertex at origin and axis along positive direction of y-axis.
Solution
Let P denote the family of parabolas and let S (0. a) be the focus of a member of the given family, where a is an arbitrary constant.
∴ equation of family P is
a2 = 4 a y ...(1)
Differentiating both sides w.r.t. x, we get.
Putting value of 4a in (1), we get,
which is the required differential equation.