Jawabanmu

2013-12-29T20:15:26+07:00
Rumus Sn = 1/2 n [2a + (n-1)b]

Soal A . S10 = 1/2 . 10 (2.2 +9.6)
                    = 5 (4+54)
                    = 290
Soal B . S20 = 1/2 . 20 (2.-22+19.6)
                    = 10 (-44+114)
                    = 700

Ket . a = suku pertama
b = beda
n = banyaknya suku