Plot.plot({
x:{domain:[-10,10]},
y:{domain:[-2,2]},
marks:[
Plot.ruleX([-10]),
Plot.ruleY([0]),
Plot.line(x,{x:x,y:y,stroke:"red"}),
Plot.dot([[x0,f(x0)]],{r:5, fill:"black"}),
Plot.line(x,{x:x,y:Y1}),
Plot.line(x,{x:x,y:Y2, strokeDasharray:"5,5", stroke: "blue"})
]
})