Question

the nth term of an ap an = 3n -1 ,find the sum of the first 20 terms​

Answer 1

an=3n-1

a1=2

a2=5

here a=2, d=3

sum=n×(2a+(n-1)×d)/2

sum of first 20 elements n=20

sum = 10 × (4+19×3)

sum = 610