A truss ABC supports a load W at joint B, as shown in the figure. The length

Question:

A truss ABC supports a load W at joint B, as shown in the figure. The length L1 of member AB is fixed, but the length of strut BC varies as the angle ( is changed. Strut BC has a solid circular cross section. Joint B restrained against displacement perpendicular to the plane of the truss.
Assuming the collapse occurs by Euler buckling of the strut, determine the angle ( for minimum weight of the strut.