Integral von $$$t \cos{\left(t^{2} \right)}$$$

Bestimme $$$\int t \cos{\left(t^{2} \right)}\, dt$$$.

Sei $$$u=t^{2}$$$.

Dann $$$du=\left(t^{2}\right)^{\prime }dt = 2 t dt$$$ (die Schritte sind » zu sehen), und es gilt $$$t dt = \frac{du}{2}$$$.

Somit,

$${\color{red}{\int{t \cos{\left(t^{2} \right)} d t}}} = {\color{red}{\int{\frac{\cos{\left(u \right)}}{2} d u}}}$$

Wende die Konstantenfaktorregel $$$\int c f{\left(u \right)}\, du = c \int f{\left(u \right)}\, du$$$ mit $$$c=\frac{1}{2}$$$ und $$$f{\left(u \right)} = \cos{\left(u \right)}$$$ an:

$${\color{red}{\int{\frac{\cos{\left(u \right)}}{2} d u}}} = {\color{red}{\left(\frac{\int{\cos{\left(u \right)} d u}}{2}\right)}}$$

Das Integral des Kosinus ist $$$\int{\cos{\left(u \right)} d u} = \sin{\left(u \right)}$$$:

$$\frac{{\color{red}{\int{\cos{\left(u \right)} d u}}}}{2} = \frac{{\color{red}{\sin{\left(u \right)}}}}{2}$$

Zur Erinnerung: $$$u=t^{2}$$$:

$$\frac{\sin{\left({\color{red}{u}} \right)}}{2} = \frac{\sin{\left({\color{red}{t^{2}}} \right)}}{2}$$

Daher,

$$\int{t \cos{\left(t^{2} \right)} d t} = \frac{\sin{\left(t^{2} \right)}}{2}$$

Fügen Sie die Integrationskonstante hinzu:

$$\int{t \cos{\left(t^{2} \right)} d t} = \frac{\sin{\left(t^{2} \right)}}{2}+C$$

$$$\int t \cos{\left(t^{2} \right)}\, dt = \frac{\sin{\left(t^{2} \right)}}{2} + C$$$A