$$\color{rgb(0,0,0)}x$$

$$\color{rgb(255,102,102)}y$$

$$\color{rgb(255,102,102)}y=x^2$$

$$\color{rgb(0,0,255)}a$$

$$\color{rgb(0,0,255)}b$$

$$\color{rgb(127,0,0)} \begin{array}{l} {a<b } \\ {a^2<b^2} \end{array}$$

$$\color{rgb(0,0,255)}\Rightarrow \text{Variations sur }[0;+\infty[$$

$$\color{rgb(0,0,255)}\Rightarrow \text{Variations sur }]-\infty;0]$$

$$\color{rgb(0,0,255)}a^2$$

$$\color{rgb(0,0,255)}b^2$$