hitung jumlah deret aritmetika berikut 100+95+90+85....sampai 20 suku

Mapel : Matematika
Bab : Barisan dan deret

100 + 95 + 90 + 85

a = 100
b = 95 - 100 = - 5

Sn = n/2(2a + (n-1) b)
S20 = 20/2 (2(100) + (20 - 1) -5)
S20 = 10 (200 + 19 × -5)
S20 = 10 ( 200 + -95)
S20 = 10(105)
S20 = 1.050

SUku pertama (a) = 100
beda = 95 - 100 = -5
Ditanyakan S20 (jumlah 20 suku pertama)

[tex]S_2_0= \frac{n}{2} [2a+(n-1)b] \\ S_2_0= \frac{20}{2} [2(100)+(20-1)(-5)] \\ S_2_0= 10 [200-95] = 10 (105) = 1.050[/tex]