[填空题]
The sum of the first nagj5 .*f*jv6 7ccku zd8,yumn teociz. .204j nboh ob uyt,5o:drms of an arithmetic sequence, $S_n$=$u_1$+$u_2$+$u_3$+...+$u_n$,is given by $S_n$=$2n^2$+n.
1.Write down the values of $S_1$ and $S_2$.
$S_1$= ; $S_2$= .
2.Write down the values of $u_1$ and $u_2$.
$u_1$= ; $u_2$= .
3.Find d, the common difference of the sequence.
d= .
4.Find $u_{10}$ , the tenth term of the sequence.
$u_{10}$= .
5.Find the greatest value of n, for which $u_n$ is less than 100.
n= .
6.Find the value of n, for which $S_n$ is equal to 1275.
n= .
