Show that a1, a2,…, an form an AP where an is defined as below.an = 9 – 5n. Also, find the sum of the first 15 terms in each case.

Show that a1, a2,…, an form an AP where an is defined as below.

(ii) an = 9 – 5n. Also, find the sum of the first 15 terms in each case.