Establish the following vector inequalities geometrically or otherwise:
(a) |a + b| ā¤ |a| + |b|
(b) |a + b| ā„ ||a| ā |b||
(c) |a ā b| ā¤ |a| + |b|
(d) |a ā b| ā„ ||a| ā |b||
When does the equality sign above apply?