Answer:
[tex]\large \boxed{\sf C. \ \frac{n+1}{2} (3n+2)}[/tex]
Step-by-step explanation:
[tex]\displaystyle \frac{n}{2} (3n-1)[/tex]
To find the (n+1)st term, replace the n variable with n+1.
[tex]\displaystyle \frac{n+1}{2} (3(n+1)-1)[/tex]
Expand brackets.
[tex]\displaystyle \frac{n+1}{2} (3n+3-1)[/tex]
Subtract like terms in brackets.
[tex]\displaystyle \frac{n+1}{2} (3n+2)[/tex]
