Here is some information about the sequence.
Worked Solution & Mark Scheme (4 marks)
Comparing terms with 3n2:
n = 1: 10 - 3(1)2 = 7 M1
n = 2: 17 - 3(2)2 = 5
n = 3: 30 - 3(3)2 = 3 M1
The sequence of differences 7, 5, 3, … has first difference -2, giving -2n + 9
Therefore, the nth term is 3n2 - 2n + 9. A1