Consider a line L passing through the points P(1, 2, 1) and Q(2, 1, -1). If the mirror image of the point A(2, 2, 2) in the line L is ( , , ), then + + 6 is equal to .
Answer
6
Solution
PQ = (1, -1, -2); any point of L: F(1 + t, 2 - t, 1 - 2t)
[figure]
AF = (t - 1, -t, -1 - 2t) PQ
(t - 1) + t + 2(1 + 2t) = 0 6t + 1 = 0 t = - 16
foot F ( 56, 136, 43 )
F is the mid-point of AA′: ( , , ) = 2F - A = (- 13, 73, 23 )
+ + 6 = - 13 + 73 + 4 = 6
Answer: 6