Find the missing terms of the arithmetic sequence.​ (Hint: The arithmetic mean of the first and fifth terms is the third​ term.)

Question

2, a2, a3, a4, -30....

Answer 1

30 = 2 + 4d

28 = 4d

7 = d

2, 9, 16, 23, 30

Answer 2

2, a2, a3, a4, 30

common difference = d = an-an-1 for any two consecutive terms

such as 30-a4 = a4-a3 = a3-a2= a2 -2

that's 4d between 30 and 2

30-2 =28 = 4d

d = 28/4 = 7

2, 2+7, 2+14, 2+21, 2+28

2, 9, 16, 23, 30