Problem:
Reflection

For given three points p1, p2, p, find the reflection point x of p onto p1p2.

Input

xp1 yp1 xp2 yp2
q
xp0 yp0
xp1 yp1
...
xpq−1 ypq−1

In the first line, integer coordinates of p1 and p2 are given. Then, q queries are given for integer coordinates of p.

Output

For each query, print the coordinate of the reflection point x. The output values should be in a decimal fraction with an error less than 0.00000001.

Constraints

1 ≤ q ≤ 1000

-10000 ≤ xi, yi ≤ 10000

p1 and p2 are not identical.

Sample Input 1

0 0 2 0
3
-1 1
0 1
1 1

Sample Output 1

-1.0000000000 -1.0000000000
0.0000000000 -1.0000000000
1.0000000000 -1.0000000000

Sample Input 2

0 0 3 4
3
2 5
1 4
0 3

Sample Output 2

4.2400000000 3.3200000000
3.5600000000 2.0800000000
2.8800000000 0.8400000000

Solution in Ruby (judge verdict: Accepted)

require 'matrix'
p1x, p1y, p2x, p2y = gets.split.map &:to_i
p1 = Vector[ p1x, p1y ]
p1p2 = Vector[ p2x - p1x, p2y - p1y ]
q = gets.to_i
q.times do
  px, py = gets.split.map &:to_i
  p = Vector[ px, py ]
  p1p = Vector[ px - p1x, py - p1y ]
  p1t_norm = p1p.inner_product(p1p2) / p1p2.norm
  t = p1 + p1p2 * ( p1t_norm / p1p2.norm )
  pt = Vector[ t[0] - px, t[1] - py ]
  u = p + pt * 2
  puts "%.8f %.8f" % [ u[0], u[1] ] 
end