已知等差数列的前n项和为Sn，且Sp=Sq（p≠q，p、q∈N），则Sp+q=______．
设Sp=Sq=m，
=x，则（Sp+q p+q
，p）、（m p
，q）、m q
（x，p+q）在同一直线上，
由两点斜率相等可知
=q-p
-m q m p p+q-p x- m p
解得x=0，
∵p+q≠0
∴Sp+q=0；
故答案为：0．
| 阅读短文，用方框中所给单词的适当形式填空。方框中有一个单词是多余的。 | |
Shanghai last year and fell in love with it. I think it's 2________ a beautiful city. As a 3_______, I think I will meet lots of 4______ people. I think I'll live in an apartment with some of my best friends, because I don't like living 5_______. I'll have pets. I can't have any pets now because my mother hates 6________, and our apartment is too 7 . Maybe I'll have many different pets 8_______ I get a big apartment. And I think I'll go to America for further study some day. |