A hint to get started
Combine parallelogram vectors, an internal angle and a nearest point
With respect to origin O, A and C have position vectors and , respectively. B is such that OABC is a parallelogram.
(i) Write down the position vector of B.
(ii) Find angle OAB to the nearest degree.
(iii) Find a vector equation of line AB.
D has position vector .
(iv) Verify that D is on line AB.
(v) Find the position vector of the point on line AB closest to O.
CJC · Lecture · Example 27
Choose a point on the line and a nonzero direction; keep one parameter consistent across all components.