TITIK STATIONER
Titik stationer
\begin{equation*} f'(x) = 0 \end{equation*}
Jenis titik stationer
\begin{equation*} \begin{split} f''(x) & > 0 \quad \text{titik minimum lokal} \\\\ f''(x) & < 0 \quad \text{titik maksimum lokal} \\\\ f''(x) & = 0 \quad \text{titik belok} \end{split} \end{equation*}
Contoh
Diketahui kurva \(f(x)=\dfrac{1}{5} x^{5}-\dfrac{1}{3} x^{3}\).
Tentukan titik-titik stasioner kurva dan jenisnya.
Koordinat titik stasioner
\begin{equation*}
\begin{split}
& f(x)=\frac{1}{5} x^{5}-\frac{1}{3} x^{3} \\\\
& f' (x) =0\\\\
& x^{4}-x^{2} =0\\\\
& x^{2} \:.\: (x^{2}-1) =0\\\\
& x^2 \:.\: (x+1) \:.\: (x-1) =0\\\\
& x=0 \text{ atau } x=-1 \text{ atau } x=1
\end{split}
\end{equation*}
Titik x = −1
\begin{equation*} \begin{split} f(-1) & = \frac{1}{5} (-1)^{5}-\frac{1}{3} (-1)^{3} \\\\ f(-1) & = \frac{2}{15} \end{split} \end{equation*}
Koordinat titik \(\left(-1,\dfrac{2}{15} \right)\)
Titik x = 0
\begin{equation*} \begin{split} f(0) & = \frac{1}{5} (0)^{5}-\frac{1}{3} (0)^{3} \\\\ f(0) & = 0 \\\\ \end{split} \end{equation*}
Koordinat titik \((0,0)\)
Titik x = 1
\begin{equation*} \begin{split} f(1) & = \frac{1}{5} (1)^{5}-\frac{1}{3} (1)^{3} \\\\ f(1) & = -\frac{2}{15} \end{split} \end{equation*}
Koordinat titik \(\left(1,-\dfrac{2}{15} \right)\)
Menentukan jenis titik stasioner dengan uji turunan kedua:
\begin{equation*}
\begin{split}
f(x) & =\frac{1}{5} x^{5}-\frac{1}{3} x^{3} \\\\
f'(x) & = x^{4}-x^{2} \\\\
f''(x)&=4x^{3}-2x
\end{split}
\end{equation*}
Titik \(\left (-1,\dfrac{2}{15} \right)\)
\begin{equation*} \begin{split} f''(-1) & = 4(-1)^{3}-2(-1) \\\\ f''(-1) & =-2 \: {\color[RGB]{0,0,255} < 0 \quad \text{(maksimum)}} \end{split} \end{equation*}
Titik \((0,0)\)
\begin{equation*} \begin{split} f''(0)&=4(0)^{3}-2(0) \\\\ f''(0)& =0 \quad {\color[RGB]{0,0,255} \text{(titik belok)}} \end{split} \end{equation*}
Titik \(\left(1,-\dfrac{2}{15} \right)\)
\begin{equation*} \begin{split} f''(1) & =4(1)^{3}-2(1) \\\\ f''(1) & = 2 \: {\color[RGB]{0,0,255} > 0 \quad \text{(minimum)}} \end{split} \end{equation*}