given,a=2, d=8 ,Sn=90 ,find n and an
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Answered by
3
sn =(n/2) (2a+(n-1) d)
90= n/2(4+(n-1) 8)
180=8n²-4n
8n²-4n-180
therefore n=5
90= n/2(4+(n-1) 8)
180=8n²-4n
8n²-4n-180
therefore n=5
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Answered by
14
sn=90
sn=n/2 (2a+(n-1)d)
90=n/2 (2×2+(n-1)8)
180/n=+ 4×8n-8
180/n=8n-4
180=8n^2-4n
8n^2-4n-180=0
2n^2-n-45=0
2n^2-10n+9n-45=4
2n (n-5)+9 (n-5)=0
(2n+9) (n-5)=0
n= -9/2 or n=5
but n cannot be negative.
so, n=5
an=a+(n-1)d
as=2+(s-1)8
as=2+4×8
as=2+32=34
i Hope this can help you!
sn=n/2 (2a+(n-1)d)
90=n/2 (2×2+(n-1)8)
180/n=+ 4×8n-8
180/n=8n-4
180=8n^2-4n
8n^2-4n-180=0
2n^2-n-45=0
2n^2-10n+9n-45=4
2n (n-5)+9 (n-5)=0
(2n+9) (n-5)=0
n= -9/2 or n=5
but n cannot be negative.
so, n=5
an=a+(n-1)d
as=2+(s-1)8
as=2+4×8
as=2+32=34
i Hope this can help you!
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