7. Find x and y such that 3; x; y form an arithmetic sequence and x; y; 25 form a geometric sequence.

8. T₁ = (k−1)a + (k+1)b is the general term of an arithmetic
sequence.

8.1)
Write down the first 3 terms in terms of an and b.

8.2)
If the common difference is 3 and (T₁)² = T3 - 4, calculate possible values of an and b.

8.3)
Write down the sequence(s).