how many terms of the Arithmetic sequence 8,12,16,.. should be added to get the sum 540
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answer is 15.
>540=n÷2[(2×8) +(n-1)4]
>1080=n[16+4n-4]
>1080=12n+4n.n
>n.n+3n-270=0
>n.n+18n-15n-270=0
>n=-18 or n=15
as n in positive integer
so answer is 15th term
>540=n÷2[(2×8) +(n-1)4]
>1080=n[16+4n-4]
>1080=12n+4n.n
>n.n+3n-270=0
>n.n+18n-15n-270=0
>n=-18 or n=15
as n in positive integer
so answer is 15th term
ijab:
S15=15÷2(8+64)=15÷2×72=15×36=540
ok
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