1.

The orthogonal trajectories of the family of curves an `a^(n-1)y = x^n` are given by (A) `x^n+n^2y=constant` (B) `ny^2+x^2=constant` (C) `n^2x+y^n=constant` (D) `y=x`A. `x^(n)+n^(2)y`= constantB. `ny^(2)+x^(2)`= constantC. `n^(2)x+y^(n)`= constantD. `n^(2)x-y^(n)`= constant

Answer» Correct Answer - B
The equaiton of the given family of curves is
`a^(n-1)y=x^(n)" …(i)"`
`rArr" "(n-1)loga+logy=n logx`
Differentiaing w.r.t. x, we get
`(1)/(y)(dy)/(dx)=(n)/(x)" …(ii)"`
This is the differential equation of the family of curves given in (i).
The differential equation of the orthogonal trajectories of (i) is obtained by replacing `(dy)/(dx)by-(dx)/(dy)` in (ii).
Replacing `(dy)/(dx)by-(dx)/(dy)` in (ii), we get
`(1)/(y)xx-(dx)/(dy)=(n)/(x)rArr xdx +ny dy=0`
On integrating, we get
`(x^(2))/(2)+n(y^(2))/(2)=C rArr x^(2)+ny^(2)=2C`


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