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To add to Justin's answer here, I think the graph was both helpful and misleading. The way we interpret where the maximum and minimum are on the graph, we tend to put them in the middle of our peaks and valleys,, so if we compare this to what we see on the graph vs our numbers, the visual max/min doesn't quite align correctly with those points $(0,0) (1,0) (-1,0) (0,1) (0,-1)$.

I agree with all of the mathematics above though, and that is also the answer that i calculated.