根据下列两组x、y的值，求出代数式的值． （1）； （2）满足的x、y的值．

（1）当时，···················································································· （1分） ，·································································· （3分） .······························································································· （4分） （2）由非负性可知········································································ （6分） 当时， ，···································································· （7分） .          （8分） 【解析】 试题分析：（1）把x、y的值代入代数式，运用有理数的混合运算求值． （2）利用绝对值和完全平方都大于或等于0得出x、y的值. 考点：代数式求值；绝对值；完全平方．