F1 = 1. ;

    m = 1. ;

    omeg0 = 1.0;

    A = (F1/m)/(omeg0^2 - omeg1^2);

    Plot[{A}, {omeg1, 0,  .5*omeg0}, PlotPoints -> 100, 
        PlotLabel -> "Amplitude of the Driven Oscillator", 
        AspectRatio ->  .45, 
        AxesLabel -> {"omeg1", "A"}];