Given a=2,d=8,sn=90 find n and an explain
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Answered by
1
a=2
d=8
sum=90
so apply formulae
s=n/2(2a+(n-1)d)
90=n/2(2×2+(n-1)×8)
90=n/2(4+8n-8)
90=n/2(-4+8n)
180=-4n+8n^2
so
8n^2-4n-180=0
8n^2-40n+36n-180=0
8n(n-5)+36(n-5)=0
(n-5)(8n+36)=0
so
n=5 or n=-4
but n cannot be in negitive so
n=5
d=8
sum=90
so apply formulae
s=n/2(2a+(n-1)d)
90=n/2(2×2+(n-1)×8)
90=n/2(4+8n-8)
90=n/2(-4+8n)
180=-4n+8n^2
so
8n^2-4n-180=0
8n^2-40n+36n-180=0
8n(n-5)+36(n-5)=0
(n-5)(8n+36)=0
so
n=5 or n=-4
but n cannot be in negitive so
n=5
Answered by
0
Answer:
Sn = (n/2)(2a+(n-1)d)
90 = (n/2)(4+(n-1)8)
180 = n(8n-4)
180 = 8n^2-4n
8n^2-4n-180 = 0
n=5
An = 2+4*8=34
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