先化简，再求值：－2x2－2[3y2－2(x2－y2)＋6]，其中x＝－1，y＝－2．

问题详情：

先化简，再求值：－2x2－2[3y2－2(x2－ y2)＋6]，其中x＝－1，y＝－2．

【回答】

－2x2－2[3y2－2(x2－y2)＋6]

=－2x2－2[3y2－2x2  + 2y2＋6]································································· 3分

=－2x2－6y2 + 4x2 －4y2－12···································································· 4分

=2x2－10y2 －12 ····················································································· 5分 

当x＝－1，y＝－2时

原式=2×（－1）2－10×（－2）2－12

   =2×1－10×4－12

    =2－40－12

=－50······································································································· 6分 

知识点：整式的加减

题型：解答题