The normal modes of this system are products of trigonometric functions. (For linear systems, the time dependance of a normal mode is always sinusoidal, but the spatial dependence need not be.) Specifically, for this system a normal mode is described byyi(x,t)=Ai sin(2p*x/?i)sin(2pfi*t)find the three lowest normal mode frequencies f1 , f2 , and f3 . express the frequencies in terms of l , v , and any constants. list them in increasing order, separated by commas.