Plot[Sin[Pi t], {t,-1,1}]

Plot[{2Cos[Pi t]+.6Cos[4 Pi t],2Cos[Pi t]}, {t,-1,1},PlotStyle ->{{Black,Thick},{ Blue,Dashed}} , AxesStyle -> Directive[Large]]

Plot[{2Cos[Pi t]+.6Cos[4 Pi t]}, {t,-1,1},PlotStyle ->{{Black,Thick},{ Blue,Dashed}} , AxesStyle -> Directive[Large]]

Plot[{2Cos[Pi t]+.6Cos[4 Pi t]}, {t,-3,3},PlotStyle ->{{Black,Thick},{ Blue,Dashed}} , AxesStyle -> Directive[Large]]