Let ( , , ) be the co-ordinates of the foot of the perpendicular drawn from the point (5, 4, 2) on the line r = (- i + 3 j + k) + (2 i + 3 j - k). Then the length of the projection of the vector i + j + k on the vector 6 i + 2 j + 3 k is :
- 187
- 157
- 4
- 3
Answer
(1) 187
Solution
General point of the line: F(-1 + 2 , 3 + 3 , 1 - )
PF from P(5, 4, 2): (2 - 6, 3 - 1, - - 1)
PF (2, 3, -1): 2(2 - 6) + 3(3 - 1) - (- - 1) = 0
14 - 14 = 0 = 1
( , , ) = (1, 6, 0)
Projection on 6 i + 2 j + 3 k = (1)(6) + (6)(2) + (0)(3) 36 + 4 + 9 = 187
Answer: (1)