Parabola,,Could you help me please??

Answer:
[tex]\large \boxed{\sf \bf \sqrt{\dfrac{10}{3}}}[/tex]
Dimension of the rectangle is
[tex]2\times\sqrt{\dfrac{10}{3}}\\ \\10-\dfrac{10}{3}=\dfrac{20}{3}[/tex]
Step-by-step explanation:
Hello,
[tex]\text{The area is }2x(1-x^2) \\ \\\text{The derivative is }2(10-x^2)+2x(-2x)=2(10-3x^2)\\\\\text{The derivative is }0\text{ for} 10-3x^2=0 \\\text{so for } x=\sqrt{\dfrac{10}{3}}[/tex]
Thanks