Dik:Deret Aritmatika=5+10+15+20 Dit:Tentukanlah=a)S14,b)S51,c)S100

Sn = 1/2 x n x ( U1 + Un )

a) S14
cari u14 → a+(n-1)b = 5+(14-1)5 = 5+65 = 70
S14 = 1/2 x 14 x (5+70)
= 7x75
= 525

b) S51
cari u51 → a+(n-1)b =5+(51-1)5=5+250= 255
S51 = 1/2 x 51 x (5+255)
= 25,5 x 260
= 6630

c) S100
cari u100→a+(n-1)b= 5+(100-1)5= 5+495 =500
S100 = 1/2 x 100 x (5+500)
= 50 x505
= 25.250