in an arithmetic progression if an =2n+1 then find the sum of first 20terms​

1 thought on “in an arithmetic progression if an =2n+1 then find the sum of first 20terms​”

1. Answer:

   an =2n+1 S20=?

   Step-by-step explanation:

   let n=1

   a1=2×1+1

   a=2+1

   =3

   let n=2

   a2=2×2+1

   a2=4+1

   a2=5

   d=a2-a

   d=5-3

   d=2

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

   S20=20/2(2×3+19×2)

   S20=10(6+38)

   S20=10×44

   S20=440.

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