Now, denote as F A and F B the components of the forces that are perpendicular to the radial segments PA and PB. These forces are given by F A = F A ⋅ ⋅ e A ⊥ ⊥ , F B = F B ⋅ ⋅ e B ⊥ ⊥ . This notation and the principle of virtual work yield the formula for the generalized force as Q = a F A − − b F B = 0.