We've already taken its derivative, but we'll do it again. G prime of x is equal to two plus fundamental theorem of calculus, the derivative of this right over here is just f of x. And if we have the second derivative of g, g prime prime of x, this is equal to derivative of two is just zero. And the derivative of f of x is f prime of x. So asking where this has a sign change, asking where our second derivative has a sign change, is equivalent to asking where does the first derivative of f have a sign change. And asking where the first derivative of f has a sign change is equivalent to saying where does the slope of f have a sign change? You can view this as the slope or the instantaneous slope of f. So we want to know when the slope of f has a sign change.