8,12,6 is an ap find s20 and s35 using the formula sn=n/2[2a + (n-1)d]

1 thought on “8,12,6 is an ap find s20 and s35 using the formula sn=n/2[2a + (n-1)d]”

1. Step-by-step explanation:

   Solution:

   Given a=6d=3

   S

   27

   =

   2

   n

   [2a+(n−1)d]

   S

   27

   =

   2

   27

   [2×6+26×3]

   =

   2

   27

   [12+78]

   =

   2

   27

   [90]

   =1,215

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