题目

先化简，再求值：3（2x﹣y）2+（2x+y）（2x﹣y）+（﹣3x）（4x﹣3y），其中x＝﹣1，y＝1． 答案：9． 【解析】 先利用完全平方公式，平方差公式，整式的乘法计算方法计算后合并，再进一步代入求得数值即可． 【详解】 原式＝12x2﹣12xy+3y2+4x2﹣y2﹣12x2+9xy ＝4x2﹣3xy+2y2； 当x＝﹣1，y＝1时， 原式＝4×（﹣1）2﹣3×（﹣1）×1+2×12＝9． 【点睛】 此题考查整式的混合运算，注意先利用计算公式计算化简读短文，判断正(√)误(×)。      It's 11: 30. I'm in the canteen. I have rice, beef and potatoes for lunch. It's cold today. I wear my new sweater. It's cheap. But it's very nice. It's only 25 yuan. I like it very much. (     ) 1. It's eleven thirteen.(     ) 2. I have rice, beef and tomatoes for lunch.(     ) 3. It's not hot today.(     ) 4. My sweater is twenty-four yuan.(     ) 5. The sweater is very expensive.