Show that the three lines with direction cosines
12
3
4
4
12
3
3
4
12
,
,
;
,
,
;
,
,
13
13
13
13
13
13
13
13
13
−
−
−
 are mutually perpendicular 2 Show that the line through the points (1, – 1, 2), (3, 4, – 2) is perpendicular to the
line through the points (0, 3, 2) and (3, 5, 6) 3