In order for action potentials to travel to their intended destination they must cross synapses. These synapses are the spaces between neurones' axon terminals
This is an example of the product rule. In this, y=uv and dy/dx = u(dv/dx) + v(du/dx) u = sin2x so du/dx = 2 * cos2x = 2cos2x v = (3x-1)4