2020年全国各地市中考数学模拟试题分类汇编3整式 下载本文

当x=2时,原式=2×(2)2+1=5. ··················································· 7分 3x?2?x?1)?2x?2x?1 2、x?1(3x2?1x?2答案:原式?(?)?x?1x?1(x?1)2 ………………………………1分

?(x?2)(x?2)(x?1)2??x?1x?2 …………………………………………3分

??x2?x?2 …………………………………………4分

3、(2020昆山一模)计算:已知x2-4=0,求代数式x(x+1)2-x(x2+x)-x-7的值. 答案:

4、(2020年北京市延庆县一诊考试)化简求值:当2x2?3x?1?0时 ,求

(x?2)2?x(x?5)?2x?8的值.

解:?x?2??x?x?5??2x?8 =x2?4x?4?x2?5x?2x?8 =2x2?3x?4 ∵2x2?3x?1=0

∴2x2?3x??1

∴原式=2x2?3x?4=?1?4??5

25、(2020年福州模拟卷) (2) 先化简,再求值:(x+1)2+x(x-2),其中x=2. (2)解:(x+1)2+x(x-2) =x2+2x+1+x2-2x ······································································· 4分 =2x2+1, ···················································································· 5分

当x=2时,原式=2×(2)2+1=5. ··················································· 7分