Find the values of (2j^)·(-4k^)

Let, A=2i^ and B=(-4k^)A=2i^+0j^+0k^ and B=0i^-0j^-4k^Also, A·B=ABcos θSince both A and B are on the same axis, The value of θ is 90.Therefore, A·B=ABcos θ⇒A·B=(2)(-4)cos90°=0