Analysis-Kurvendiskussion-Ganzrationale Funktion
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Beispiel Nr: 55
$\begin{array}{l} \text{Gesucht:}\\ \text{Definitions- und Wertebereich}
\\ \text{Grenzwerte}
\\ \text{Symmetrie}
\\ \text{Nullstellen - Schnittpunkt mit der x-Achse}
\\ \text{Ableitungen - Stammfunktion}
\\ \text{Extremwerte - Monotonie}
\\ \text{Wendepunkte - Krümmung}
\\ \text{Stammfunktion}
\\ \text{Eingeschlossene Fläche mit der x-Achse} \\ \text{Funktion:}f\left(x\right)=-5\frac{2}{5}x^3-37\frac{4}{5}x^2-75\frac{3}{5}x-43\frac{1}{5} \ <br/>
\bullet \text{Funktion/Ableitungen/Stammfunktion} \\ f\left(x\right)=-5\frac{2}{5}x^3-37\frac{4}{5}x^2-75\frac{3}{5}x-43\frac{1}{5}=-5\frac{2}{5}(x+4)(x+2)(x+1)\\
f'\left(x\right)=-16\frac{1}{5}x^2-75\frac{3}{5}x-75\frac{3}{5}=-16\frac{1}{5}(x+3,22)(x+1,45)\\
f''\left(x\right)=-32\frac{2}{5}x-75\frac{3}{5}=-32\frac{2}{5}(x+2\frac{1}{3})\\
f'''\left(x\right)=-32\frac{2}{5}
\\
F(x)=\int_{}^{}(-5\frac{2}{5}x^3-37\frac{4}{5}x^2-75\frac{3}{5}x-43\frac{1}{5})dx=-1\frac{7}{20}x^4-12\frac{3}{5}x^3-37\frac{4}{5}x^2-43\frac{1}{5}x+c
\\ \\ \bullet\text{Definitions- und Wertebereich:}\\\qquad \mathbb{D} = \mathbb{R} \qquad \mathbb{W} = \mathbb{R} \\
\\ \bullet \text{Grenzwerte:} \\
f(x)=x^3(-5\frac{2}{5}-\dfrac{37\frac{4}{5}}{x}-\dfrac{75\frac{3}{5}}{x^2}-\dfrac{43\frac{1}{5}}{x^3}) \\
\lim\limits_{x \rightarrow \infty}{f\left(x\right)}=[-5\frac{2}{5}\cdot \infty^3]=-\infty \\\lim\limits_{x \rightarrow -\infty}{f\left(x\right)}=[-5\frac{2}{5}\cdot (-\infty)^3]=\infty \\
\\ \bullet \text{Symmetrie zum Ursprung oder zur y-Achse } \\f\left(-x\right)=-5\frac{2}{5}\cdot (-x)^{3}-37\frac{4}{5}\cdot (-x)^{2}-75\frac{3}{5}\cdot (-x)-43\frac{1}{5} \\
\text{keine Symmetrie zur y-Achse und zum Ursprung }
\\
\\ \bullet \text{Nullstellen / Schnittpunkt mit der x-Achse:} \\f(x)=-5\frac{2}{5}x^3-37\frac{4}{5}x^2-75\frac{3}{5}x-43\frac{1}{5} = 0 \\ \\-5\frac{2}{5}x^3-37\frac{4}{5}x^2-75\frac{3}{5}x-43\frac{1}{5}=0 \\\\ \text{Nullstelle für Polynmomdivision erraten:}-2\\
\,\small \begin{matrix} (-5\frac{2}{5}x^3&-37\frac{4}{5}x^2&-75\frac{3}{5}x&-43\frac{1}{5}&):( x +2 )=-5\frac{2}{5}x^2 -27x -21\frac{3}{5} \\
\,-(-5\frac{2}{5}x^3&-10\frac{4}{5}x^2) \\ \hline
&-27x^2&-75\frac{3}{5}x&-43\frac{1}{5}&\\
&-(-27x^2&-54x) \\ \hline
&&-21\frac{3}{5}x&-43\frac{1}{5}&\\
&&-(-21\frac{3}{5}x&-43\frac{1}{5}) \\ \hline
&&&0\\
\end{matrix} \\ \normalsize \\
\\
-5\frac{2}{5}x^{2}-27x-21\frac{3}{5} =0
\\
x_{1/2}=\displaystyle\frac{+27 \pm\sqrt{\left(-27\right)^{2}-4\cdot \left(-5\frac{2}{5}\right) \cdot \left(-21\frac{3}{5}\right)}}{2\cdot\left(-5\frac{2}{5}\right)}
\\
x_{1/2}=\displaystyle \frac{+27 \pm\sqrt{262\frac{11}{25}}}{-10\frac{4}{5}}
\\
x_{1/2}=\displaystyle \frac{27 \pm16\frac{1}{5}}{-10\frac{4}{5}}
\\
x_{1}=\displaystyle \frac{27 +16\frac{1}{5}}{-10\frac{4}{5}} \qquad x_{2}=\displaystyle \frac{27 -16\frac{1}{5}}{-10\frac{4}{5}}
\\
x_{1}=-4 \qquad x_{2}=-1
\\ \underline{x_1=-4; \quad1\text{-fache Nullstelle}} \\\underline{x_2=-2; \quad1\text{-fache Nullstelle}} \\\underline{x_3=-1; \quad1\text{-fache Nullstelle}} \\
\\ \bullet \text{Vorzeichentabelle:} \\
\begin{array}{|c|c|c|c|c|c|c|c|c|c||}
\hline
& x < &-4&< x <&-2&< x <&-1&< x\\
\hline
f(x)&+&0&-&0&+&0&-\\
\hline
\end{array}\\ \\
\underline{\quad x \in ]-\infty;-4[\quad \cup \quad]-2;-1[\quad f(x)>0 \quad \text{oberhalb der x-Achse}}\\ \\
\underline{\quad x \in ]-4;-2[\quad \cup \quad]-1;\infty[\quad f(x)<0 \quad \text{unterhalb der x-Achse}} \\
\\ \bullet \text{Extremwerte/Hochpunkte/Tiefpunkte:} \\f'(x)=-16\frac{1}{5}x^2-75\frac{3}{5}x-75\frac{3}{5} = 0 \\ \\
\\
-16\frac{1}{5}x^{2}-75\frac{3}{5}x-75\frac{3}{5} =0
\\
x_{1/2}=\displaystyle\frac{+75\frac{3}{5} \pm\sqrt{\left(-75\frac{3}{5}\right)^{2}-4\cdot \left(-16\frac{1}{5}\right) \cdot \left(-75\frac{3}{5}\right)}}{2\cdot\left(-16\frac{1}{5}\right)}
\\
x_{1/2}=\displaystyle \frac{+75\frac{3}{5} \pm\sqrt{816\frac{12}{25}}}{-32\frac{2}{5}}
\\
x_{1/2}=\displaystyle \frac{75\frac{3}{5} \pm28,6}{-32\frac{2}{5}}
\\
x_{1}=\displaystyle \frac{75\frac{3}{5} +28,6}{-32\frac{2}{5}} \qquad x_{2}=\displaystyle \frac{75\frac{3}{5} -28,6}{-32\frac{2}{5}}
\\
x_{1}=-3,22 \qquad x_{2}=-1,45
\\ \underline{x_4=-3,22; \quad1\text{-fache Nullstelle}} \\\underline{x_5=-1,45; \quad1\text{-fache Nullstelle}} \\f''(-3,22)=28,6>0 \Rightarrow \underline{\text{Tiefpunkt:} (-3,22/-11,4)} \\
f''(-1,45)=-28,6 \\
f''(-1,45)<0 \Rightarrow \underline{\text{Hochpunkt:} (-1,45/3,41)} \\
\\
\bullet\text{Monotonie/ streng monoton steigend (sms)/streng monoton fallend (smf) } \\
\begin{array}{|c|c|c|c|c|c|c||}
\hline
& x < &-3,22&< x <&-1,45&< x\\
\hline
f'(x)&-&0&+&0&-\\
\hline
\end{array}\\ \\
\underline{\quad x \in ]-3,22;-1,45[\quad f'(x)>0 \quad \text{streng monoton steigend }}\\ \\
\underline{\quad x \in ]-\infty;-3,22[\quad \cup \quad]-1,45;\infty[\quad f'(x)<0 \quad \text{streng monoton fallend }}
\\
\\\bullet\text{Wendepunkte:} \\f''(x)=-32\frac{2}{5}x-75\frac{3}{5} = 0 \\ \\
-32\frac{2}{5} x-75\frac{3}{5} =0 \qquad /+75\frac{3}{5} \\
-32\frac{2}{5} x= 75\frac{3}{5} \qquad /:\left(-32\frac{2}{5}\right) \\
x=\displaystyle\frac{75\frac{3}{5}}{-32\frac{2}{5}}\\
x=-2\frac{1}{3}
\\ \underline{x_6=-2\frac{1}{3}; \quad1\text{-fache Nullstelle}} \\f'''(-2\frac{1}{3})=-4\\
f'''(-2\frac{1}{3}) \neq 0 \Rightarrow \\
\underline{\text{Wendepunkt:} (-2\frac{1}{3}/-4)}\\
\bullet\text{Kruemmung} \\
\begin{array}{|c|c|c|c||}
\hline
& x < &-2\frac{1}{3}&< x\\
\hline
f''(x)&+&0&-\\
\hline
\end{array}\\ \\
\underline{\quad x \in ]-\infty;-2\frac{1}{3}[\quad f''(x)>0 \quad \text{linksgekrümmt}}\\ \\
\underline{\quad x \in ]-2\frac{1}{3};\infty[\quad f''(x)<0 \quad \text{rechtsgekrümmt}}\\
\\
\bullet\text{Eingeschlossene Fläche mit der x-Achse} \\A=\int_{-4}^{-2}\left(-5\frac{2}{5}x^3-37\frac{4}{5}x^2-75\frac{3}{5}x-43\frac{1}{5}\right)dx=\left[-1\frac{7}{20}x^4-12\frac{3}{5}x^3-37\frac{4}{5}x^2-43\frac{1}{5}x\right]_{-4}^{-2}
\\ =\left(-1\frac{7}{20}\cdot (-2)^{4}-12\frac{3}{5}\cdot (-2)^{3}-37\frac{4}{5}\cdot (-2)^{2}-43\frac{1}{5}\cdot (-2)\right)-\left(-1\frac{7}{20}\cdot (-4)^{4}-12\frac{3}{5}\cdot (-4)^{3}-37\frac{4}{5}\cdot (-4)^{2}-43\frac{1}{5}\cdot (-4)\right)
\\ =\left(14\frac{2}{5}\right)-\left(28\frac{4}{5}\right)=-14\frac{2}{5}
\\ A=\int_{-2}^{-1}\left(-5\frac{2}{5}x^3-37\frac{4}{5}x^2-75\frac{3}{5}x-43\frac{1}{5}\right)dx=\left[-1\frac{7}{20}x^4-12\frac{3}{5}x^3-37\frac{4}{5}x^2-43\frac{1}{5}x\right]_{-2}^{-1}
\\ =\left(-1\frac{7}{20}\cdot (-1)^{4}-12\frac{3}{5}\cdot (-1)^{3}-37\frac{4}{5}\cdot (-1)^{2}-43\frac{1}{5}\cdot (-1)\right)-\left(-1\frac{7}{20}\cdot (-2)^{4}-12\frac{3}{5}\cdot (-2)^{3}-37\frac{4}{5}\cdot (-2)^{2}-43\frac{1}{5}\cdot (-2)\right)
\\ =\left(16\frac{13}{20}\right)-\left(14\frac{2}{5}\right)=2\frac{1}{4}
\\ \\
\end{array}$