` vec u , vec va n d vec w` are three non-coplanar unit vecrtors anf `alpha,betaa n dgamma` are the angles between` vec ua n d vec v , vec va n d vec w ,a n d vec wa n d vec u ,` respectively, and ` vec x , vec ya n d vec z` are unit vectors along the bisectors of the angles `alpha,betaa n dgamma` , respectively. Prove that `[ vec xxx vec y vec yxx vec z vec zxx vec x]=1/(16)[ vec u vec v vec w]^2sec^2alpha/2sec^2beta/2sec^2gamma/2dot`