I understand that this is via inner products. However, I don't quite understand the relation and how to find $v_2, v_3, v_4$ from the matrix.
For part (b), I hypothesise that if $v_4$ is a zero vector, then it would mean that $v_1, v_2, v_3 and v_4$ are colinear. Is it correct to conclude it this way or am I heading in the wrong direction?
I appreciate any help!