If the image of the point P(1, 0, 3) in the line joining the points A(4, 7, 1) and B(3, 5, 3) is Q( , , ), then + + is equal to :
- 463
- 18
- 13
- 473
Answer
(1) 463
Solution
Direction ratios of AB: (3 - 4, 5 - 7, 3 - 1) = (-1, -2, 2)
Any point on AB: M(4 - t, 7 - 2t, 1 + 2t)
PM = (3 - t, 7 - 2t, -2 + 2t)
M is the foot of the perpendicular PM (-1, -2, 2) = 0
-(3 - t) - 2(7 - 2t) + 2(-2 + 2t) = 0
9t - 21 = 0 t = 73
M ( 53, 73, 173 )
M is the mid-point of PQ Q = 2M − P
= ( 103 - 1, 143 - 0, 343 - 3 ) = ( 73, 143, 253 )
+ + = 7 + 14 + 253 = 463
Answer: (1)