Question 1214

Vectors I: Basics, Dot and Cross Products
2014 Paper 1 Question 3 Variant

Question

(i)
Find a unit vector n{\mathbf{n}} such that
n×(8i+4j+k)=0.\mathbf{n} \times (8 \mathbf{i} + 4 \mathbf{j} + \mathbf{k}) = \mathbf{0}.
[2]
(ii)
Find the cosine of the acute angle between 8i+4j+k{8 \mathbf{i} + 4 \mathbf{j} + \mathbf{k}} and the z-{z\textrm{-}}axis.
[1]

Answer