Mathematics

Problem

Consider

\mathbf a = \langle 2,\!-1,\,2\rangle

and

\mathbf b = \langle k,\!-\tfrac{k}{2},\,k\rangle

. The two vectors are always parallel. For which value of

k

do they have the same magnitude and point in opposite directions? a)

k=-4

k=-2

k=2

k=-\dfrac{6\sqrt5}{5}