Known: in the arithmetic sequence {an}, A3 + A4 = 15, a2a5 = 54, tolerance d < 0, the second question 1) Finding the general term formula an of sequence {an} 1、 The arithmetic sequence is A2 + A5 = A3 + A4 = 15 a2a5=54 By Weida theorem A2, A5 are the equations X & # 178; - 15x + 54 = 0 x=6,x=9 d

Known: in the arithmetic sequence {an}, A3 + A4 = 15, a2a5 = 54, tolerance d < 0, the second question 1) Finding the general term formula an of sequence {an} 1、 The arithmetic sequence is A2 + A5 = A3 + A4 = 15 a2a5=54 By Weida theorem A2, A5 are the equations X & # 178; - 15x + 54 = 0 x=6,x=9 d

Your question is ambiguous (1) is Sn also a molecule (2) is an-3 an minus 3 or a (n-3), make it clear for you, according to my understanding, first give an answer an = 11-n Sn = 11n-n (n + 1) / 2 [Sn - (an-3)] / N = [11n-n (n + 1) / 2 - (8-N)] / N = 11 - (n + 1) / 2 - (8 / n-1) = 23 / 2 - N / 2-8 / N and N / 2 + 8 /