[tex] y= \frac{1}{2} x^2-4\\\\y=0\ \ \ \Leftrightarrow\ \ \ \frac{1}{2} x^2-4=0\ /\cdot2\ \ \ \Leftrightarrow\ \ \ x^2-8=0\\\\x^2-(2 \sqrt{2} )^2=0\ \ \ \Leftrightarrow\ \ \ (x-2 \sqrt{2} )(x+2 \sqrt{2} )=0\\\\x-2 \sqrt{2} =0\ \ \ \ \ \ \ \ or\ \ \ \ \ \ \ \ \ x+2 \sqrt{2}=0\\\\x=2 \sqrt{2}\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ x=-2 \sqrt{2[/tex]