Let `vec(a),vec(b)` and `vec(c)` be three vectors such that `vec(a) ne 0, |vec(a)|=|vec(c)|=1,|vec(b)|=4` and `|vec(b)xxvec(c)|=sqrt(15)` .If `vec(b)-2vec(c)=lambdavec(a)` , then find the value of `lambda` .

Answer

`lambda^(2)=16"or" lambda=+-4`