Line L1 passes through the point (1, 2, 3) and is parallel to z-axis. Line L2 passes through the point ( , 5, 6) and is parallel to y-axis. Let for = 1, 2, 2 < 1, the shortest distance between the two lines be 3. Then the square of the distance of the point ( 1, 2, 7) from the line L1 is
- 25
- 32
- 40
- 37
Answer
(1) 25
Solution
L1: r = ( i + 2 j + 3 k) + s k; L2: r = ( i + 5 j + 6 k) + t j
k j = - i, a2 - a1 = ( - 1) i + 3 j + 3 k
S.D. = |( a2 - a1) (- i)||- i| = | - 1| = 3
⇒ = 4 or -2 ⇒ 1 = 4, 2 = -2
Point: (4, -2, 7). L1 is the line x = 1, y = 2 (parallel to the z-axis), so the distance depends only on x and y:
d2 = (4 - 1)2 + (-2 - 2)2 = 9 + 16 = 25
Answer: (1)