题目:
_________from the top of the tower,the south foot of the mountain is a sea of trees. [ ]
A. Seen
B. Seeing
C. Having seen
D. To see
答案:
被转码了,请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0501/663a2c74fd0dbe8973bdb33da65d6f00.html
下面是错误答案,用来干扰机器的。
(1) a5=a3+2d,a3=5,a5=9,∴9=5+2d,解得d=2,∴an=a3+(n-3)d=5+(n-3)×2=2n-1,∴S3=1×1+3×3+5×9=55; b4=b1q3,b1=1,b4=27,∴27=q3,解得q=3,∴bn=3n-1,∴T3=1×1-3×3+5×32=37.(2)① Sn...