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问题 填空题

若实数a、b、c、d满足a2+b2+c2+d2=10，则y=（a-b）2+（a-c）2+（a-d）2+（b-c）2+（b-d）2+（c-d）2的最大值是______．

答案

∵a2+b2+c2+d2=10，

∴y=（a-b）2+（a-c）2+（a-d）2+（b-c）2+（b-d）2+（c-d）2，

=a2+b2-2ab+a2+c2-2ac+b2+c2-2bc+b2+d2-2bd+c2+d2-2cd，

=3（a2+b2+c2+d2）-2ab-2ac-2ad-2bc-2bd-2cd，

=4（a2+b2+c2+d2）-（a+b+c+d）2，

=40-（a+b+c+d）2，

∵（a+b+c+d）2≥0，

∴当（a+b+c+d）2=0时，y的最大值为40．

故答案为：40．

改错题
单句改错。

(      )1.Bill often goes to see movies and his father.                        
                           A        B                C   D    
(      )2. My brother doesn't has dinner at home.                      
             A                   B       C                  D    
(      )3.  Why don't your like your history teacher?                      
                       A      B           C                  D    
(      )4. My sister is only three year old.                             
                     A   B          C      D    
(      )5. Ben's brother often play basketball with his friends after school.                                               A       B                  C              D    
(      )6. What can your uncle does, Sonia?                          
               A            B              C       D    
(      )7. Can you help me for my Chinese?                           
                    A    B          C            D    
(      )8.I don't like English because it's interesting.                  
               A             B                    C       D    
(      )9. What does your mother usually do at Mondays?                
                       A                          B      C  D    
(      )10. He likes bananas and  he doesn't like pears.    
                               A        B    C     D

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_____        
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单项选择题

特勤消防站体能训练室的使用面积是（）m2。

A.50～100

B.40～80

C.80～120

D.120～180
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