Three forces with magnitudes F_a, F_b, F_c act on a point mass, pulling in unit directions a, b, c, respectively. Thr forces are in 'equilibrium' which means that
F_aa + F_bb + F_cc = 0
By taking the cross product with a, show that
F_b(a \times b) = F_c(c \times a)
and find two similar...