Solve these problems from arithmetic sequences:
For what real numbers x is the sequence 
arithmetic?
What is the sum of all natural numbers between 1000 and 10000 divisible by 17 ?
The lengths of the sides of the triangle form an arithmetic sequence, the middle measures 7.5 cm. The area of the triangle is equal to 
. Accurately calculate the lengths of the shortest and longest sides of the triangle.
Write down the first term 
, the common difference d and the general term 
of an arithmetic sequence whose sum of the first n terms is equal to 
.
and 
respectively.
