[填空题]
The third term, $u_3$ , of an arithmetic sequence is 7. The common difference of
the sequence, d, is 3.
Find $u_1$ , the first term of the sequence.
$u_1$= .
Find $u_{60}$ , the 60th term of sequence.
$u_{60}$= .
The first and fourth terms of this arithmetic sequence are the first two terms
of a geometric sequence.
Calculate the sixth term of the geometric sequence.
$u_6$= .
