If the distance of the point (a, 2, 5) from the image of the point (1, 2, 7) in the line x1= y-11= z-22 is 4, then the sum of all possible values of a is equal to :
- 11
- 9
- 6
- 4
Answer
(3) 6
Solution
Let L(t, 1+t, 2+2t) be the foot of the perpendicular from A(1, 2, 7) on the line.
AL=(t-1, t-1, 2t-5) (1, 1, 2)
(t-1)+(t-1)+2(2t-5)=0 6t=12 t=2 L(2, 3, 6)
L is the mid-point of A and its image A' A'=(2 2-1, 2 3-2, 2 6-7)=(3, 4, 5)
Distance of (a, 2, 5) from A' is 4: (a-3)2+(2-4)2+(5-5)2=16
(a-3)2=12 a=3 2 3
Sum of all possible values of a=6
Answer: (3)