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u5 = 17
u10 = 32
u5 = a+(5-1)b = 17
u10= a+(10-1)b = 32
u5= a+4b = 17
u10=a+9b=32
maka,
a+4b=17 dikurangi a+9b=32
hasil=
-5b= -25
b = -25/-5
b= 5
mencari suku pertama:
(pilih salah satu suku yg telah diketahui)
misal: u5= a+4b=17
substitusikan b=5 kedalam persamaan tsb
a+4b=17
a+4(5)=17
a+20=17
a=17-20
a= -3
jumlah 20suku pertama:
gunakan rumus,
sn= n/2 (2a+(n-1))
s20 = 20/2 (2(-3) +(20-1))
= 10 ( -6+19)
= 10 (13)
=130
semoga membantu
u10 = a + 9b = 32
a + 4b = 17
a + 9b = 32 ( di krang)
-5b = -15
b = 3
a + 4(3) = 17
a + 12 = 17
a = 5
S20 = n/2 (2a + (n-1)b )
= 20/2 (2(5) + (19)3)
= 10 ( 10 + 57 )
= 10 (67)
= 670