In an RC circuit, the voltage across the resistor, V(R), is negative during discharging because the polarity of the voltage changes as the capacitor releases its stored energy. When the capacitor discharges, the end of the resistor that was previously positive becomes less than the voltage of the capacitor, resulting in a negative voltage across the resistor. This behavior is a fundamental aspect of how capacitors and resistors interact in a circuit. The discussion emphasizes the importance of understanding voltage polarity in both charging and discharging phases. Overall, the relationship between voltage and current in RC circuits is crucial for analyzing their behavior.