[填空题]
In an arithmetic sequekrhfr)ep8 zlhulw: q+i;1;3cw1+ rl-gy(hf knce, the third term is w*j;.0y pvd)wzg y w1c41 and the ninth term is 23 .
1. Find the common difference.
2. Find the first term.
3. Find the smallest value of n such that $S_{n}<0$ .
