NCERT Solutions
Class 12 Maths
Three Dimensional Geometry

Ex.11.2 Q.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).
Let AB be the line joining the points, (1, −1, 2) and (3, 4, − 2), and CD be the line joining the points, (0, 3, 2) and (3, 5, 6).
The direction ratios, a1, b1, c1 of AB are (3 − 1), (4 − (−1)), and (−2 − 2) i.e., 2, 5 and −4.
The direction ratios, a2, b2, c2 of CD are (3 − 0), (5 − 3), and (6 −2) i.e., 3, 2, and 4.
AB and CD will be perpendicular to each other, if a1a2 + b1b2+ c1c2 = 0
Now, a1a2 + b1b2+ c1c2 = 2 * 3 + 5 * 2 + (− 4) * 4
= 6 + 10 − 16
= 0
Therefore, AB and CD are perpendicular to each other.