A hint to get started
Find an axis crossing and the origin-to-line distance
Line l passes through A=(1,2,−1) and B=(2,a,1).
(i) Show that l cuts the x-axis when a=−2. marks
(ii) Find the length of projection of OA onto l and hence the shortest distance from the origin to l. marks
[2008/NYJC/Promo/5]
CJC · Review problems · Question 2
An x-axis crossing has y=z=0, not just one zero coordinate.