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