Answer:
S₃₁ = 2077
Step-by-step explanation:
the sum to n terms of an arithmetic sequence is
[tex]S_{n}[/tex] = [tex]\frac{n}{2}[/tex] [ 2a₁ + (n - 1)d ]
where a₁ is the first term and d the common difference
here a₁ = 7 and d = a₂ - a₁ = 11 - 7 = 4 , then
S₃₁ = [tex]\frac{31}{2}[/tex] [ (2 × 7) + (30 × 4) ]
= 15.5 (14 + 120)
= 15.5 × 134
= 2077
