Question

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

Answer 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.