For an LCR circuit driven at frequency ω, the equation reads
L di/dt+Ri+q/C=vi=vm sinωt
(i) Multiply the equation by i and simplify where possible.
(ii) Interpret each term physically.
(iii) Cast the equation in the form of a conservation of energy statement.
(iv) Intergrate the equation over one cycle to find that the phase difference between v and i must be acute.