You should essentially differentiate the quadratic $x^2 + 2x -4$ w.r.t. $x$ and plug in $x=2$. But since you have tagged this "precalculus", do you know how to differentiate a (polynomial) function? – 2011-12-17
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For the sake of completeness, it would be nice to have an answer that showed the differentiating approach – 2015-09-27