[填空题]
The fifth term, $u_5$ , of a geometric sequence is 25. The eleventh term, $u_{11}$ , of the same sequence is 49.
Find d, the common difference of the sequence.
d= .
Find $u_1$ , the first term of the sequence.
$u_1$= .
Find $S_{100}$ ,the sum of the first 100 terms of the sequence.
$S_{100}$= .
