Let the point A be the foot of perpendicular drawn from the point P(a, b, 0) on the line x-12= y-21= z- 3. If the midpoint of the line segment PA is (0, 34, - 14 ), then the value of a2+b2+ 2 is equal to :
- 1
- 2
- 6
- 9
Answer
(1) 1
Solution
Midpoint of PA is (0, 34, - 14 ) and P(a, b, 0)
A= (-a, 32-b, - 12 )
PA= (-2a, 32-2b, - 12 ) (2, 1, 3)
-4a+ 32-2b- 32=0 b=-2a
A on the line: -a=1+2t, 32-b=2+t, - 12= +3t
a=-1-2t, b=- 12-t
b=-2a - 12-t=2+4t t=- 12
a=0, b=0, =- 12+ 32=1
(Check: A (0, 32, - 12 ) gives - 12 in each ratio of the line)
a2+b2+ 2=0+0+1=1
Answer: (1)