1. When one or both of the vectors pf 1+0 and PF2 are zero vectors,

| vector pf 1+vector pf2 | = | vector pf 1 |+| vector pf2 |。

2. When the vector pf6+0 and the vector PF2 are non-zero vectors,

| vector PF 1+ vector PF2 | represents the length of PQ in the parallelogram pf 1 qf2 with pf1and PF2 as adjacent sides.

| vector PF 1 | | vector PF2 | represents the sum of the lengths of line segment PF 1 and line segment PF2.

∵AF 1QF2 is a parallelogram, ∴ pf 1 = f2q, obviously: pf2+f2q > pq.

∴:| vector pf 1+vector pf2 |