To the left, I state a conventional definition of the derivative of the function in question. When x is negative as it is on the second line of the derivation, the numerator (|x + dx| - |x|) is -dx because dx is always a positive number. Thus the derivative is -1. On the third line when x is positive, this simplifies to +1.
Plate subduction occurs when two tectonic plates meet at a convergent plate boundary (the plates are crashing into one another) and at least one of the plates is denser than the underlying mantle. If neither plate is denser than the underlying mantle the plates will create a non-volcanic mountain range like the Himalaya.
This is a particularly interesting area to study because we can observe two types of plate boundaries (divergent and convergent) and their processes in very close proximity. A divergent boundary occurs when two tectonic plates move away from each other.here are three kinds of plate tectonic boundaries: divergent, convergent, and transform plate boundaries. This image shows the three main types of plate boundaries: divergent, convergent, and transform.