Question
Show that the general quartic (fourth-degree) polynomial $f(x)=x^{4}+a x^{3}+b x^{2}+c x+d$ has either zero or two inflection points, and the latter case occurs provided that $b<3 a^{2} / 8$.
Step 1
The first derivative of the function is $f'(x)=4x^{3}+3ax^{2}+2bx+c$. Show more…
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Show that the general quartic (fourth-degree) polynomial $f(x)=x^{4}+a x^{3}+b x^{2}+c x+d$ has either zero or two inflection points, and the latter case occurs provided that $b<3 a^{2} / 8.$
Show that the general quartic (fourth-degree) polynomial $f(x)=x^{4}+a x^{3}+b x^{2}+c x+d,$ where $a, b, c,$ and $d$ are real numbers, has either zero or two inflection points, and the latter case occurs provided $b<\frac{3 a^{2}}{8}$.
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Show that every polynomial function of degree 3 $f(x)=a x^{3}+b x^{2}+c x+d$ has exactly one inflection point.
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