P = (x + y + z - t) + (x + y - z + t) + (x - y + z + t) + (-x + y + z + t)
P = x + y + z - t + x + y - z + t + x - y + z + t - x + y + z + t
P = (x + x - x) + (y + y - y) + (z + z - z) + (t + t - t)
P = 2x + 2y + 2z + 2t
P = 2 (x + y + z + t)
Với x = 1; y = 10; z = 100; t = 1000, ta có:
P = 2 (1 + 10 + 100 + 1000)
P = 2 . 1111
P = 2222
Vậy P = 2222 với x = 1; y = 10; z = 100; t = 1000
