Question

Jumlah deret aritmatika berikut: 200 + 190 + 180 + 170 + ... + 90 adalah

Answer 1

A = 200
b = -10
Un = a + (n-1)b
90 = 200 + (n-1)(-10
90 = 200 - 10n + 10
n = 12
S12 = 12/2 (2(200) +(12-1)(-10))
       = 6 (400 - 110)
       = 6 (290)
       = 1.740

Answer 2

U1 = 200 b = -10 90 = 200 + ( n -1) (-10) 90 = 200 + 10 -10 n 10n = 210 -90 n = 120 / 10 = 12 Sn = n /2 ( a + Un ) S12 = 12/2 ( 200 + 90 ) = 6 ( 290) = 1740