I've been given this question and am struggling to complete it.

Relative to a fixed origin, O, the points A and B have position vectors

(i + 5j -1k) and (6i + 3j - 6k) respectively

Find in exact, simplified form,

(i) the cosine of angle AOB - i have done this and it comes out as root 3 over 3

(ii) the area of the triangle

(iii) the shortest distance from A to the line OB

Any help on this would be very much appreciated. Thanks