问题
选择题
已知等差数列{an}中，|a3|＝|a9|，公差d<0，Sn是数列{an}的前n项和，则( )
A．S5>S6
B．S5<S6
C．S6＝0
D．S5＝S6
答案
答案：D
∵d<0，|a3|＝|a9|，∴a3>0，a9<0，且a3＋a9＝0，∴a6＝0，a5>0，a7<0，∴S5＝S6.
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已知等差数列{an}中，|a3|＝|a9|，公差d<0，Sn是数列{an}的前n项和，则( )
A．S5>S6
B．S5<S6
C．S6＝0
D．S5＝S6
答案：D
∵d<0，|a3|＝|a9|，∴a3>0，a9<0，且a3＋a9＝0，∴a6＝0，a5>0，a7<0，∴S5＝S6.
| 读一读，写一写。 | |
| Peter goes to the library at ten in the morning. Then he has lunch with his friends at one fifteen in the canteen. He goes home at six and has dinner at seven ten. On Sunday, Peter goes to a music class at two in the afternoon. Then he plays computer games, at eight.
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