If a, b and c are the lengths of the sides of a triangle then
if a ≤ b ≤ c, then a + b > c.
1. a ≤ 3 ≤ 8 then a + 3 > 8 → a > 8 - 3 → a > 5 FALSE, because a ≤ 3.
2. 3 ≤ a ≤ 8 then 3 + a > 8 → a > 5 therefore 5 < a ≤ 8
3. 3 ≤ 8 ≤ a then 3 + 8 > a → 11 > a → a < 11 therefore 8 ≤ a < 11.
Answer: 5 < a < 11 → S = (5, 11)
