1. 410 + 430 + 450 +... s20 : ... 2. 906 + 900 + 894 + ... s30 : ...

Bab Barisan dan Deret
Kelas 9 SMP
Matematika

Aritmatika Naik

a = 410
b = 430 - 410
   = 20

U20 = 410 + (20 - 1) 20
        = 410 + 380
        = 790

S20 = 20/2 (410 + 790)
       = 10 (1200)
       = 12000


Aritmatika Turun


a = 906
b = 900 - 906
   = -6


U30 = 906 + (30 - 1) -6
       = 906 + -174
       = 732

S30 = 30/2 (906 + 732)
       = 15 (1638)
       = 24570

Semoga Membantu!!!

Nomor 1 :
Sn = n/2 (2a + (n-1)b)
S20 = 20/2 (2 x 410 + (20-1)20)
S20 = 10 ( 820 + 19 x 20)
S20 = 10 (820 + 380)
S20 = 10 x 1200
S20 = 12.000

Nomor 2
S30 = 30/2 (2 x 906 + (30 - 1)-6)
S30 = 15 (1812 + 29 x -6)
S30 = 15 (1812 + (-174))
S30 = 15 x 1638
S30 = 24570