Question

Tentukan banyak suku dan jumlah barisan aritmatika berikut
a.4+9+14+19+.......+104
b.72+66+60+54+...+12
c.-12-8-4-0+...+128
d.-3-7-11-15....-17

Answer 1

1. un = a + (n-1).b
4 + (n-1).5
4+5n
n = 20

sn = 1/2.n +(2.a (n-1).b
= 10 + 8 .19.5
= 10 + 760
= 770

selebihnya ikutin rumus ajj pasti ketemu

Answer 2

Rumusnya n=(Un-a+b)/b
Rumus Sn=n/2(a+Un)

a). a=4, b=5, Un=104
n=(104-4+5)/5=105/5=21
S21=21/2(4+104)=10,5(108)=1134

b). a=72, b=-6, Un=12
n=(12-72-6)/-6=-66/-6=11
S11=11/2(72+12)=5,5(84)=462

c). a=-12, b=4, Un=128
n=(128-(-12)+4)/4=144/4=36
S36=36/2(-12+128)=18(116)=2088

satu lg coba sendiri ya