问题
填空题
两个等差数列{an}和{bn}的前n项和分别为An和Bn，且
|
答案
令n=13，所以A13=
=13a7；13(a1+a13) 2
同理Bn=
=13b7，13(b1+b13) 2
则
=A13 B13
=13a7 13b7
=a7 b7
=7×13+45 13+3
．7 2
故答案为：7 2
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两个等差数列{an}和{bn}的前n项和分别为An和Bn，且
|
令n=13，所以A13=
=13a7；13(a1+a13) 2
同理Bn=
=13b7，13(b1+b13) 2
则
=A13 B13
=13a7 13b7
=a7 b7
=7×13+45 13+3
．7 2
故答案为：7 2
| 完形填空。 | |||
| Look at this picture. This is a photo __1__ my family. There are __2__ people in the picture: my father, my mother, my brother, my sister and __3__ .__4__ father is very happy every day. My mother __5__ near (在……旁边) my father. The boy beside (在……旁边) my mother is my __6__ . The __7__ near my mother is my little sister.__8__ is very clever and cute. Everyone likes her very much. Who is __9__ boy in the middle (在中间)? Ah! It is me.__10__ love my family very much. | |||
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