设an=an^2+bn+c,依题意
2=a+b+c.
1=4a+2b+c,
0.5=16a+4b+c,
相减得-1=3a+b,
-0.5=12a+2b,
解得a=1/4,b=-7/4,c=7/2.
∴an=(1/4)(n^2-7n+14),
a3=0.5.
2,1,<>,0.5空中可填0.5.
猜你喜欢
- 1照样子在括号里填上合适的词想一想这些词组有什么共同特点
- 2275nm的紫外波长处有最大吸收的物质是什么
- 3制作一个容积是V的圆柱形饮料罐,当底面半径为多少时所用材料最少?
- 4betty works ( ) of the three .most carefully ,more carefully ,more careful ,the most carefully
- 5用英文根据下列提示写一篇介绍你理想学校的文章,80字
- 6what do you usually have for breakfast
- 7句子开头用waiting for me?还是wait for me?
- 8英语连词成句 if go you a to will have the party you great time
- 9一个椭圆,左顶点为A,上顶点为B ,左焦点为F,F 到直线AB距离为d,d等于a乘OB长度,求椭圆离心率
- 10不等式4x-3>7x+6的最大整数解是