Note: This post will be constantly updated to add more formula.

Nomenclatures:

V = voltage, volts
I = current, amperes
R = resistance, ohms,~Omega
P = power, watts
P = power, watts
X = reactance, ohms,~Omega
Z = impedance, ohms,~Omega

I. Direct Current

V=I*R
I=V/R
R=V/I
P=I*V
P={I^2}*R
P={V^2}/R

II. AC Current

P=I*V*cos~{theta}
Z=V/I
Z=sqrt{{R^2}+{X^2}}
PF=cos~{theta}
PF=R/Z
PF=R/{sqrt{{R^2}+{X^2}}
PF=P/{I*V}