given a is equal to 2 ,d is equal to 8 ,sn is equal to 90 find n and an
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Given,
a=2 , d=8 , sn=90
To find :- n and an
Solution:-
sn=n/2[2a+(n-1)d]
90=n/2[2(2)+(n-1)8]
90×2=n[4+8n-8]
180=n[8n-4]
8n^2-4n-180=0
2n^2-n-45=0
2n(n-5)+9(n-5)=0
(n-5)(2n+9)=0
n=5
an=a+(n-1)d
an=2+(5-1)8
an=2+32
an=34
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