Euler's formula

:  a general engineering formula relating to the strength of a long strut and obtained by mathematical analysis assuming the strut to be initially very slightly bent and neglecting the (dy/dx)² term in the curvature equation: P = cπ²EI/l², where P = axial load, E = Young's modulus, I = moment of inertia of transverse section of strut, l = length of strut, and c = a constant depending upon the manner of fixing the ends