设个体域为整数集z，确定下列各公式的真值．
&nBsp;&nBsp;(1)(x²＞0)．&nBsp;&nBsp;(2)(x²=0)．
&nBsp;&nBsp;(3)(x²≥x)．&nBsp;&nBsp;(4)(x²＜y)．
&nBsp;&nBsp;(5)(x＜y²)．&nBsp;&nBsp;(6)(x+y=0)．
&nBsp;&nBsp;(7)(x²+y²=6)．&nBsp;&nBsp;(8)(z=(x+y)/2)．