> mod1=lm(mpg~poly(disp,2)+hp+cyl,data=mtcars)
> mod2=lm(mpg~poly(disp,3)+hp+cyl,data=mtcars)
> anova(mod1,mod2)

Analysis of Variance Table

Model 1: mpg ~ poly(disp, 2) + hp + cyl
Model 2: mpg ~ poly(disp, 3) + hp + cyl
  Res.Df   RSS Df Sum of Sq      F    Pr(>F)
1     27 222.5
2     26 106.1  1    116.41 28.526 1.369e-05 ***
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Signif. codes:  0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’ 1