in a graph, an intercept means a "touch" or a crossing, namely an x-intercept is when the graph touches the x-axis, thus is called an x-intercept, also goes by the name of the "solutions" or "zeros" or "roots".
when that happens, y = 0. Likewise, when an y-intercept happens, namely the y-axis gets intercepted by the graph, then x = 0.
to get the x-intercepts, simply set y = 0 and solve for "x".
likewise, to get the y-intercepts, simply set x = 0 and solve for "y".
so let's do so in this case for the x-intercepts,
[tex]\bf y=\cfrac{1}{2}(x-2)^2-8\implies \stackrel{y}{0}=\cfrac{1}{2}(x-2)^2-8\implies 8=\cfrac{(x-2)^2}{2}
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16=(x-2)^2\implies \pm\sqrt{16}=x-2\implies \pm 4= x-2\implies \pm 4 +2 = x[/tex]
and you get those two from there, and you know how much that is surely.