A horizontal comparison line

A horizontal comparison line

TGM Original
To solve f(x)>d, draw y=f(x) and y=d, identify their intersections, and select the portions above the line. For <, select below; include boundary points for <= or >=. The roots of f alone do not locate the intersections when d 0. For f(x)=x(x-1)(x+1), comparison with y=6 gives x3-x-6=(x-2)(x2+2x+3). The quadratic is (x+1)2+2>0, so there is one intersection at (2,6). The graph lies above y=6 exactly when x>2.

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