= Solution
Fast <ion-channel inactivation> would reduce the outward <potassium> <electric current> just when it normally repolarizes the axon. Since $C_m\dot V_m=I_{\rm applied}-I_{\rm Na}-I_K-I_{\rm leak}$, a reduction of positive $I_K$ makes the falling slope less negative. With other mechanisms unchanged, the <action potential> is generally broader and its after-hyperpolarization is weaker. A plateau or slow return is possible until <sodium> <ion-channel inactivation>, leakage, or another outward conductance restores the resting <membrane potential>. The precise trace depends on those remaining currents; rapid <potassium> inactivation alone does not determine a unique waveform.
\Image[/past-exam-of-the-biological-physics-course-of-the-university-of-oxford/2015-membrane-and-waiting-times.png]
{title=Original schematic <action potential> broadening and two-state relaxation and sequential-transition <probability densities>}
The left panel is a qualitative sketch of this comparison, not a fit or a reconstruction of the missing historical recording.
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