问题
问答题
已知等差数列an中,a3a7=-16,a4+a6=0,求an前n项和Sn.
答案
参考答案:
设{an}的公差为d,则
即
解得
或
因此Sn=-8n+n(n-1)=n(n-9),或Sn=8n-n(n-1)=-n(n-9)
已知等差数列an中,a3a7=-16,a4+a6=0,求an前n项和Sn.
参考答案:
设{an}的公差为d,则
即
解得
或
因此Sn=-8n+n(n-1)=n(n-9),或Sn=8n-n(n-1)=-n(n-9)
选词填空 | |
2. __________ regard cows and bulls as the spirit. 3. More and more __________ products have been sold all over the world. 4. Three __________ of the workers in this factory come from the countryside. 5. The __________ of washing one's hands before a meal is that it prevents illness. |