Let the line L1 be parallel to the vector -3 i + 2 j + 4 k and pass through the point (2, 6, 7), and the line L2 be parallel to the vector 2 i + j + 3 k and pass through the point (4, 3, 5). If the line L3 is parallel to the vector -3 i + 5 j + 16 k and intersects the lines L1 and L2 at the points C and D, respectively, then | CD |2 is equal to:
- 290
- 171
- 89
- 312
Answer
(1) 290
Solution
General points: C(2 - 3s, 6 + 2s, 7 + 4s) on L1, D(4 + 2t, 3 + t, 5 + 3t) on L2
CD = (2 + 2t + 3s, -3 + t - 2s, -2 + 3t - 4s)
∵ CD -3 i + 5 j + 16 k, let CD = (-3, 5, 16):
2 + 2t + 3s = -3 ...(i)
-3 + t - 2s = 5 ...(ii)
-2 + 3t - 4s = 16 ...(iii)
From (ii): t = 5 + 3 + 2s
In (i): 8 + 10 + 7s = -3 7s = -13 - 8
In (iii): 7 + 15 + 2s = 16 2s = - 7
7( - 7)2 = -13 - 8 33 = 33 = 1
CD = (-3, 5, 16)
| CD |2 = 9 + 25 + 256 = 290
Answer: (1)