In the equal ratio sequence an, if a1 + A2 = 3. A3 + A4 = 27. And Q > 0. An and Sn (2) In the arithmetic sequence an, if a3a7 = 12, A2 + A8 = 8, and d > 0, find an and Sn

In the equal ratio sequence an, if a1 + A2 = 3. A3 + A4 = 27. And Q > 0. An and Sn (2) In the arithmetic sequence an, if a3a7 = 12, A2 + A8 = 8, and d > 0, find an and Sn

A1 + A2 = a1 + a1q = 3 ①, A3 + A4 = q ^ 2 (a1 + a1q) = 27 ②. From ① and ②, we can see that q = 1 / 3, a1 + 1 / 3A1 = 3, A1 = 9 / 4An = 9 / 4 (1 / 3) ^ n-1, Sn = (1-9 / 4 * 3 ^ n) / 2 / 3a3 * A7 = 12, A2 + A8 = A3 + A7 = 8, and A3 = 8-a7 is brought in. We get (8-a7) * A7 = 12, the solution is that A7 = 6 or A7 = 2, and d > 0, so, a7 = 6a3 =