- 试题详情及答案解析
- (2014•湖北模拟)实数ai(i=1,2,3,4,5,6)满足(a2﹣a1)2+(a3﹣a2)2+(a4﹣a3)2+(a5﹣a4)2+(a6﹣a5)2=1则(a5+a6)﹣(a1+a4)的最大值为( )
A.3 | B.2 | C. | D.1 |
- 答案:B
- 试题分析:由柯西不等式可得:[(a2﹣a1)2+(a3﹣a2)2+(a4﹣a3)2+(a5﹣a4)2+(a6﹣a5)2](1+1+1+4+1)≥[(a2﹣a1)+(a3﹣a2)+(a4﹣a3)+2(a5﹣a4)+(a6﹣a5)]2,结合条件,即可得出结论.
解:由柯西不等式可得:
[(a2﹣a1)2+(a3﹣a2)2+(a4﹣a3)2+(a5﹣a4)2+(a6﹣a5)2](1+1+1+4+1)
≥[(a2﹣a1)+(a3﹣a2)+(a4﹣a3)+2(a5﹣a4)+(a6﹣a5)]2=[(a5+a6)﹣(a1+a4)]2,
∴[(a5+a6)﹣(a1+a4)]2≤8,
∴(a5+a6)﹣(a1+a4)≤2,
∴(a5+a6)﹣(a1+a4)的最大值为2,
故选B.
点评:本题考查柯西不等式,考查学生分析解决问题的能力,利用[(a2﹣a1)2+(a3﹣a2)2+(a4﹣a3)2+(a5﹣a4)2+(a6﹣a5)2](1+1+1+4+1)≥[(a2﹣a1)+(a3﹣a2)+(a4﹣a3)+2(a5﹣a4)+(a6﹣a5)]2,是解题的关键.