Answer:
3n² + 8n
Step-by-step explanation:
∑ (5 + 6r )
= ∑ 5 + 6 ∑ r
= 5n + 6 × [tex]\frac{1}{2}[/tex] n(n + 1)
= 5n + 3n(n + 1)
= 5n + 3n² + 3n
= 3n² + 8n
