Which Formula Should I Use for Calculating Power in an AC Circuit?

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In calculating power in an AC circuit, the formula P = Vrms.Irms.cosφ is used for real or active power, measured in watts (W). This formula accounts for the root mean square (RMS) values of voltage and current, as well as the power factor (cosφ). The instantaneous power can be calculated using P = V.I, which gives the apparent power in volt-amperes (VA). Understanding the distinction between real and instantaneous power is crucial for accurate electrical analysis. The choice of formula depends on whether the focus is on average power or instantaneous power.
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When the teacher ask me to find real power of an AC Circuit, which formula should i use ?
Should i use P = V.I or P = Vrms.Irms.cosφ ?
 
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P = Vrms.Irms.cosφ
 
Real or average or active power = Vrms.Irms.cosφ (W)
Instantaneous power = V.I (VA)
 

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