Answer: First Option is correct.
Step-by-step explanation:
Since we have given that
[tex]\sum_{n=1}^{n=\infty}(3+an)[/tex]
Here, a = 3
So, our sequence becomes,
[tex]3+a,3+2a,3+3a,................[/tex]
So, we can see that there is a common difference i.e. 'd'.
[tex]d=a_2-a_1=3+2a-(3+a)=3+2a-3-a=a[/tex]
So, it becomes an arithmetic progression.
Hence, First Option is correct.
