1)
|b| ≦ a, then -a ≦ b ≦ a
and conversely if -a ≦ b ≦ a (a ≧ 0), then |b| ≦ a.
2)
Let a ≧ 0. If |b| ≧ a,
then b ≧ a or b ≦ -a, the converse is also ture
is the above statement also true for :
|b| < a, then -a < b < a
and conversely if -a < b < a (a > 0), then |b| < a. ?
Let a > 0. If |b| > a,
then b > a or b < -a, the converse is also ture
更新1:
≦ .... is < or = ≧ ... is > or = the inequality notation