When a periodical phenomenon can be described by a sinusoid, you can find the corresponding function by determining:
the equilibrium ;
the amplitude (maximum deviation from the equlibrium);
the period ;
the horizontal translation (w.r.t. the standard graph) .
Two function rules are possible:
Note that the values for , and are the same for both, but that the values of are not. The translation with respect to the standard sine is different from the one with respect to the standard cosine.