if `overset(to)(b) \' and \' overset(to)(c )` are any two non- collinear unit vectors and `overset

if `overset(to)(b) \" and \" overset(to)(c )` are any two non- collinear unit vectors and `overset(to)(a)` is any vector then `(overset(to)(a).overset(to)(b))overset(to)(b).(overset(to)(a).overset(to)(c )) overset(to)(c ) + .(overset(to)(a).(overset(to)(b)xxoverset(to)(c)))/(|overset(to)(b)xxoverset(to)(c)|^(2)).(overset(to)(b)xxoverset(to)(c))=.........`