The line L1 is parallel to the vector a = -3 i + 2 j + 4 k and passes through the point (7, 6, 2) and the line L2 is parallel to the vector b = 2 i + j + 3 k and passes through the point (5, 3, 4). The shortest distance between the lines L1 and L2 is :
- 23 38
- 21 38
- 23 57
- 21 57
Answer
(1) 23 38
Solution
a b = vmatrix i & j & k \ -3 & 2 & 4 \ 2 & 1 & 3 vmatrix
= (6 - 4) i - (-9 - 8) j + (-3 - 4) k = 2 i + 17 j - 7 k
| a b| = 4 + 289 + 49 = 342 = 3 38
Vector joining the given points: (5 - 7) i + (3 - 6) j + (4 - 2) k = -2 i - 3 j + 2 k
SD = |(-2 i - 3 j + 2 k) (2 i + 17 j - 7 k)|| a b|
= |-4 - 51 - 14|3 38 = 693 38 = 23 38
Answer: (1)