Respuesta :

carlosego
For this case we have an equation of the form:
 d = Rcos (wt)
 Where,
 R: amplitude
 w: angular frequency
 We have the following equation:
 d = 9cos (pi / 2t)
 The frequency is:
 w = pi / 2
 Answer:
 the frequency is:
 w = pi / 2

On apex the answer is 1/4