Establish the following inequalities geometrically or otherwise ,
(a) ` | vec A + vec B| lt= | vec A | + |vec B|` ,
(b) ` | vec A + vec B| gt= ||vec A|- | vec B||`
(C )` | vec A- vec B| lt= | vec A| + |vec B|`
(d) `| vec A- vec B| gt= || vec A| - | vec B||`
When does the equality sign above apply ?

Explanation

Hint : The sum (difference ) of any two sides of a trangle is never less third side . Equality holds for collinear vectors.