Paragraph for Question Nos. 17 to 19 Consider the lines L1 : x + 1 3 = y + 2 1 = z + 1 2 L2 : x − 2 1 = y + 2 2 = z − 3 3 1. 17. The unit vector perpendicular to both L1 and L2 is   −i^−7 j ^+7 k^ √99   −i^ −7j ^+5k^ 5√3   −i^+7j ^+5k^ 5√3   −7i^−7j ^−k^ √99   Hint Half-n-half Clue   2. 18. The shortest distance between L1 and L2 is   0   17 √3   41 5√3   17 5√3   3. 19. The distance of the point (1, 1, 1) from the plane passing through the point (–1, –2, –1) and whose normal is perpendicular to both the lines L1 and L2 is   2 √75   7 √75   13 √75   23 √75   Half-n-half Clue