# the sum of n terms of the sequence where An = 5-6n and n is a natural number

second term=5-6(2)=5-12=-7

common difference(d)= second term-first term = -7-(-1) =-7+1 = -6

Sn=n/2{2a+(n-1)d}

Sum of n terms = n/2[2(-1)+(n-1)-6]

simplifying it we get 2n-3nsquare

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