If a, b, c is an arithmetic sequence then a + c = 2b
a = 5, b = 9, c = 15
subtitute
a + c = 5 + 15 = 20
2b = 2 · 9 = 18
20 ≠ 18
Answer: The sequence 5, 9, 15 is not an arithmetic sequence.
The answer is (-2, 8) and (2, -8)
-0.35, -0.3, 0.5, 0.55
is your answer
hope this helps