Problem $3(10$ points$).$ A round Lubular column of unsupported length $t$ has outside and inside diamelors of $D$ and $d,$ respectively, and a dianctral ratio of $=\frac{d}{D}.$ Show that buckling according to the parabolie formula will occur when the outside diumeter is

where $P_{er}$ is the critical lond of the column, $S_y$ is the yield strength of the material, $C$ is the end$-$condition constant and $E$ is the modulus of elasticity of the material.