Question

If nth term of am ap is 2n+1. What is rhe sum of its first 3 terms

Answer 1

tn =a+(n-1)d
2*1+1=3
2*2+1=5
2*3+1=7
sum of n terms=n/2*(2a+(n-1)d)
a=3
d=2
n=3
3/2(6+2*2)
3/2*10
sum=15