In P(max) formula how they got **4**R

and after that how they got R(ab)

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Best answer

$R_{th}$ is the Thevenin equivalent resistance of the circuit measured across ab. For this you short circuit the battery.

Maximum power is transferred to the load across ab when this load is $R_{ab}=R_{th}$.

The power dissipated in $R_{ab}$ is $\frac{V_{ab}^2}{R_{ab}}$. I think the factor of $4$ must be a mistake.

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