Tentukan jumlah 20 Suki pertama pada deret deret aritmatika berikut a. 100+92+84+... b. 36+34+32+....

a.
U1 = a = 100
U2 = 92
b = U2 - U1 = 92 - 100 = -8

Sn = 1/2 n (2a + (n-1)b)
S20 = 1/2 × 20 (2 × 100 + 19 × (-8))
S20 = 10 (200 - 152)
S20 = 10 (48)
S20 = 480

b.
U1 = a = 36
U2 = 34
b = U2 - U1 = 34 - 36 = -2

Sn = 1/2 n (2a + (n-1)b)
S20 = 1/2 × 20 (2 × 36 + 19 × (-2))
S20 = 10 (72 - 38)
S20 = 10 (34)
S20 = 340