At x=1, the curve is almost linear so if you draw a line along the curve passing through the point on the curve where x=1, that line will be the tangent with a slope of about 2/2=1 (using the dotted squares as a guide to measurement).
A horizontal line at x=2 has a slope of zero.
At x=2, as at x=1, a line can be drawn along the curve. Its slope would be about -1 (the line leans backwards).
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