x jest odwrotnością -x
gdy x = 1 to -x = -1
gdy -x = 0,5 to x = -0,5
gdy x = 0 to -x = 0
gdy x = -1/4 to -x = 1/4
gdy -x = -3 to x = 3
gdy x = 5 i 3/5 to -x = -5 i 3/5
