okay so i was giving this question i know its 2nd order differential equations but im not sure how to approach it if some one could help i would be thankful

Question:

A column of length L is subjected to a compressive load P.
The displacement, y, at a distance x is given by the solution of EI d2y/dx2+Py=0


(i) Show that y = Acos (kx) + Bsin(kx), where k=P/EI
(ii) The critical load is the value of the load P, that will cause buckling. This critical load,
P
CR
, occurs for the boundary conditions x = 0, y = 0, and x = L, y = 0. Show that the
critical load is given by:
where n is any whole number
(Note that Sin (np) = 0, where n is any whole number).