H
hailixiro142


\forall a, b chứng minh:
1. lal - lbl \leq la+bl
2. lal - lbl \leq la-bl
3. l lal - lbl l \leq la-bl
4. la-cl \leq la-bl + lb-cl
1. lal - lbl \leq la+bl
2. lal - lbl \leq la-bl
3. l lal - lbl l \leq la-bl
4. la-cl \leq la-bl + lb-cl