Jumlah bilangan deret aritmetika berikut adalah...
2+6+10+14+...+78
pake cara ya
2+6+10+14+...+78
pake cara ya
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Jawaban:
1250
Penjelasan dengan langkah-langkah:
Rumus jumlah ke-n=
Sn=n/2(2.U1+(n-1)b)
U1=2
b=U2-U1=6-2=4
Un=U1+(n-1)b
78=2+(n-1)4
78=2+4n-4
78=-2+4n
78+2=4n
100=4n
n=25
Sn=n/2(2.U1+(n-1)b)
S25=25/2(2.2+(25-1)4)
S25=25/2(4+(24)4)
S25=25/2(4+96)
S25=25/2(100)
S25=25x50=1250