Suppose f(x)=0\displaystyle {f}'{\left({x}\right)}={0} at x=x0\displaystyle {x}={x}_{{{0}}} but nowhere else. Also assume f(x)\displaystyle {f}'{\left({x}\right)} is continuous and has the following values, where ax0b\displaystyle {a}\le{x}_{{{0}}}\le{b}:

x\displaystyle {x}a\displaystyle {a}x0\displaystyle {x}_{{{0}}}b\displaystyle {b}
f(x)\displaystyle {f}'{\left({x}\right)}4\displaystyle -{4}0\displaystyle {0}5\displaystyle -{5}


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