One side is 9.
second side (3x+1) is 28.
third side (4x-9) is 27.
A
this is an arithmetic sequence whose n th term ( explicit formula) is
= + (n - 1 )d
where d is the common difference and the first term
here d = 10 - 8 = 8 - 6 = 6 - 4 = 2 and = 4, hence
= 4 + 2(n - 1 ) = 4 + 2n - 2 = 2n + 2 → A