Hi all:
I met a question about "lines".


attach(cars)


plot(dist ~ speed)
#add the regression line to the plot
lines(fitted(lm(dist~speed)) ~ speed)


plot(dist ~ speed)
#what kind of curve does the following command add to the plot?
lines(fitted(lm(dist~speed)))


My question is :
what kind of curve does the last command add to the plot?


My guess:maybe the level of fitted values?
> range(fitted(lm(dist~speed)))
[1] -1.84946 80.73112


But from the plot,I can see the range of the curve is about 10 to 40 more or less,which is different from(-1.84946, 80.73112).So the curve must not be the fitted values.What kind of curve does the last command add to the plot then?




Many thanks for your help


My best
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