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

first term=a=5-6(1)=5-6=-1
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

  • 17
Sn = n/2 (a + an)
     = n/2 (5-6 +5-6n)
     = n/2 (4-6n)
     = n(2-3n)
Sn = -3n2+2n
  • 6
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