Question

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find the sum of n term of the sequence {an},where an=5-6n,
n € N

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Answer 1

an=5-6n
Taking n=1
a=5-6
a=-1
now, taking n=2
a2=5-6×2
a2=5-12=-7
now, d=-7-(-1)=-7+1=-6
now, Sn=n/2(2a+(n-1)d)
Sn=n/2(2×(-1)+(n-1)×(-6))
Sn=n/2(-2-6n+6)
Sn=n/2(4-6n)
Sn=n(2-3n)
Sn=2n-3n²

So,
Value of sum of nth terms is 2n-3n²