A sequence of terms u1,u2,u3 ,...is defined by\x05\x05Un = 2n+5\x05 and\x05for n >or= 1.(i)\x05Write down the values of u1,u2 and u3.(ii)\x05State what type of sequence it is.

A sequence of terms u1,u2,u3 ,...is defined by\x05\x05Un = 2n+5\x05 and\x05for n >or= 1.(i)\x05Write down the values of u1,u2 and u3.(ii)\x05State what type of sequence it is.
A sequence of terms u1,u2,u3 ,...is defined by
\x05\x05Un = 2n+5\x05 and\x05for n >or= 1.
(i)\x05Write down the values of u1,u2 and u3.
(ii)\x05State what type of sequence it is.

A sequence of terms u1,u2,u3 ,...is defined by\x05\x05Un = 2n+5\x05 and\x05for n >or= 1.(i)\x05Write down the values of u1,u2 and u3.(ii)\x05State what type of sequence it is.
u1=2X1+5=7
u2=2X2+5=9
u3=2X3+5=11
这应该是一个等差数列：this is arithmetic progression

第一题 U1=7 U=9 U=11
第二题 一次函数 即 linear function 或者等差数列：arithmetic progression

等差数列中a1=25，前n项的和为Sn，若S9=S17，n为何值时Sn最大？最大值为多少？ 2. 求3 15 35 63 99的一个通项公式 1. 设公差为d S9