We know that,
Both of these quantities are always positive. Hence, cos(ϕ) is always positive. Hence, P is always positive. Thus (a) is correct.
In case R = 0, cos(ϕ) = 0. Thus P = 0. Hence, (b) is correct.
We have established that the power supplied by the source is always positive. Here, negative power means taking energy out of the circuit. Hence, option(c) is correct.
Option (d): (d) is the opposite of (c). We have already established that source can’t take energy out of the circuit. Thus, (d) is incorrect.
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