9709 P11 - Nov 2025 - Q9 - 8 marks
9643
An arithmetic progression has first term 2, common difference \(d\), and sum of its first \(n\) terms \(S_n\). The values \(S_2-1,S_4,S_9\) are the first three terms of a second arithmetic progression.
(a) Find \(d\). [4]
(b) Find the difference between the 15th terms of the two progressions. [4]
