If the shortest distance between the lines x-12 = y-23 = z-34 and x1 = y = z-51 is 5 6, then the sum of all possible values of is
- 32
- 3
- -3
- - 32
Answer
(3) -3
Solution
Line 1: a1 = (1, 2, 3), b1 = (2, 3, 4); Line 2: a2 = (0, 0, 5), b2 = (1, , 1)
a2 - a1 = (-1, -2, 2)
b1 b2 = vmatrix i & j & k \ 2 & 3 & 4 \ 1 & & 1 vmatrix = (3 - 4 , 2, 2 - 3)
| b1 b2|2 = (3-4 )2 + 4 + (2 -3)2 = 20 2 - 36 + 22
( a2 - a1) ( b1 b2) = -(3-4 ) - 4 + 2(2 -3) = 8 - 13
|8 - 13| 20 2 - 36 + 22 = 5 6
6(64 2 - 208 + 169) = 25(20 2 - 36 + 22)
116 2 + 348 - 464 = 0
2 + 3 - 4 = 0 = 1, -4
(Both are valid; the lines are never parallel since 12 14.)
sum of all possible values of = 1 + (-4) = -3
Answer: (3)