

Signe :
Le carré d'un nombre réel est toujours positif ou nul.

\draw{168,300}{alt=Courbe
xrange -4.2,4.2
yrange -1,14
parallel -4,-2,-4,14,1,0, 9, lightblue
parallel -4,-2,4,-2,0,1, 17, lightblue
arrow -4,0,4,0,8, black
arrow 0,-2,0,14,8, black
text black, 0,-0.1 , small, 0
text black, 1,-0.1 , small, 1
text black, 2,-0.1 , small, 2
text black, 3,-0.1 , small, 3
text black, -1.1,-0.1 , small, -1
text black, -2.1,-0.1 , small, -2
text black, -3.1,-0.1 , small, -3
text black, 3.4,-0.1 , large, x

text black, -0.5,0.4, small, 0
text black, -0.5,1.4, small, 1
text black, -0.5,2.4, small, 2
text black, -0.5,3.4, small, 3
text black, -0.5,4.4, small, 4
text black, -0.5,5.4, small, 5
text black, -0.5,6.4, small, 6
text black, -0.5,7.4, small, 7
text black, -0.5,8.4, small, 8
text black, -0.5,9.4, small, 9
text black, -0.5,10.4, small,10
text black, -0.5,11.4, small,11
text black, -0.5,12.4, small,12
text black, -0.5,13.4, small,13
text black, -0.8,14, large,y

plot red, x^2
text red, 1.2,4.5, large, x
text red, 1.5,4.8, small, 2
}

   \(x)
       \(-\infty)
       
       0
       
       \(+\infty)

   \(x^2)
      \(+\infty\)
      \(\searrow \)
      0
       \(\nearrow\)
      \(+\infty\)

