If the mirror image of the point P(3,4,9) in the line x-13= y+12= z-21 is ( , , ), then 14( + + ) is :
- 102
- 138
- 132
- 108
Answer
(4) 108
Solution
Foot N on the line: N(3 +1, 2 -1, +2)
[figure]
PN=(3 -2, 2 -5, -7) (3,2,1)
3(3 -2)+2(2 -5)+( -7)=0 14 =23
( 8314, 3214, 5114 )
N is the mid-point of P and its image:
+ + =2 ( 83+32+5114 )-(3+4+9)= 1667-16= 547
14( + + )=108
Answer: (4)