|2x + 1| − x ≦ 8 https://www.wolframalpha.com/input?i=+%7C2x+%2B+1%7C+%E2%88%92+x+%E2%89%A6+8&lang=ja
|2x + 1| − x ≦ 8
https://www.wolframalpha.com/input?i=+%7C2x+%2B+1%7C+%E2%88%92+x+%E2%89%A6+8&lang=ja