Question

If the angle between the vectors A and B is theta, the value of the product (BxA)xA is equal to

Answer 1

$$\begin{gathered} Asweknowaccordingtovectortripleproduct, \\ (A\times B)\times C=-(C.B)A+(C.A)B \\ So, \\ (B\times A)\times A=-(A.A)B+(A.B)A \\ =-A^{2}B+AB\cos \theta A \\ =-A^{2}B+A^{2}B\cos \theta \\ =A^{2}B(\cos \theta -1) \end{gathered}$$