Parameters in Grapher

I am trying to plot a family of similar functions in built-in Grapher. I read that one way to do this is to write one formula for all functions to be plotted and then define the parameter by which the functions differ. For example, typing in "y=sin(ax),a={1,2,3}" should plot sin(x), sin(2x), and sin(3x) simultaneously; however, I got an error message so I am thinking the last updates changed the way to do this; in that case, how do I do that?