a diff eqn is given to me..

(x^2)((d^2)y/dx^2))+(x(dy/dx))+((kx^2)-n^2)y=0

the soultions asks to use z=kx and solve the above eqn

my doubt is..can we use y=kx to solve above eqn??how do we know about the substitution to solve such kind of diff eqns to bessels eqn..????