This matched-source-load lesson shows the special DC divider case where equal source and load resistances split voltage and dissipated power equally. The 4 ohm plus 4 ohm row and paired 9 W entries are exact only for the stated ideal resistive model, not a full bandwidth or maximum-power-transfer proof. Real interfaces add impedance variation, heating, frequency dependence, parasitics, source limits, finite precision, and measurement uncertainty.
Equal source and load resistances split voltage and dissipated power in this resistive model. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Equal resistances split the source voltage
The source resistance and load are both 4 ohm, so the load voltage is 6 volts.
VL=6V
The two resistors dissipate equal power
The load power is 9 watts, and the source resistor power is also 9 watts. This lesson claims equal splitting, not a maximum proof.