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+1 vote
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in Mathematics by (150k points)

Find the sum of n terms of an A.P.whose nth terms is given by an= 5 - 6n.

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We have, an = 5-6n
⇒ a1 = 5 - 6 x 1 = -1
So, the given sequence is an A.P with first term a = a1 = -1 and last term l = an = 5 - 6n
Therefore the sum of n terms is given by: Sn= n/2 (a+l)= n/2 (-1+5-6n)=2n-3n2

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