Steven W. answered 07/31/19
Physics Ph.D., college instructor (calc- and algebra-based)
The best answer to this, I think, is to consider an analogy with displacement. Suppose you walk three meters east, then turn and walk four meters north. You walked seven meters. But your displacement is only five meters from the starting point. Where did those other two meters "go"? Well, nowhere, in a manner of speaking. You just walked seven meters in distance to achieve a displacement of five meters. The other two meters did not "vanish." They were just additional distance when the walking was done in this configuration. This illustrates the difference between arithmetic addition (which has no way to account for direction in two or more dimensions) and vector addition (which does).
In the same way, with the forces, a total magnitude of 7 N of force was used to achieve a *net* force of 5 N, based on the two-dimensional configuration.