3. The general term of a sequence is given by: Tn = 4/2^n-1
What type of a sequence is it?

4. Determine the geometric progression with second term - 4 and fifth term 4/125

5. Determine the 10th term of an arithmetic sequence in which the 3rd term is - 4 and the 7th term is - 20.

6. If x is a real number show that the following sequence cannot be a geometric sequence:
1; x+2; 3x+3; ...