On the boundedness of solutions of the equation $u''+(1+f(t))u=0$
On the boundedness of solutions of the equation $u''+(1+f(t))u=0$
Sufficient conditions on the function $\,f\,$ are given whichensure the boundedness of the solutions of the second order linear differential equation $\,u''+(1+f(t))\,u=0\,$ as $\, t\rightarrow +\infty\,$. To do this, a suitable class of quadratic forms is introduced.