Integralen av $$$\sin{\left(44 x \right)} \sin{\left(\cos{\left(44 x \right)} \right)}$$$

Bestäm $$$\int \sin{\left(44 x \right)} \sin{\left(\cos{\left(44 x \right)} \right)}\, dx$$$.

Låt $$$u=44 x$$$ vara.

Då $$$du=\left(44 x\right)^{\prime }dx = 44 dx$$$ (stegen kan ses »), och vi har att $$$dx = \frac{du}{44}$$$.

Alltså,

$${\color{red}{\int{\sin{\left(44 x \right)} \sin{\left(\cos{\left(44 x \right)} \right)} d x}}} = {\color{red}{\int{\frac{\sin{\left(u \right)} \sin{\left(\cos{\left(u \right)} \right)}}{44} d u}}}$$

Tillämpa konstantfaktorregeln $$$\int c f{\left(u \right)}\, du = c \int f{\left(u \right)}\, du$$$ med $$$c=\frac{1}{44}$$$ och $$$f{\left(u \right)} = \sin{\left(u \right)} \sin{\left(\cos{\left(u \right)} \right)}$$$:

$${\color{red}{\int{\frac{\sin{\left(u \right)} \sin{\left(\cos{\left(u \right)} \right)}}{44} d u}}} = {\color{red}{\left(\frac{\int{\sin{\left(u \right)} \sin{\left(\cos{\left(u \right)} \right)} d u}}{44}\right)}}$$

Låt $$$v=\cos{\left(u \right)}$$$ vara.

Då $$$dv=\left(\cos{\left(u \right)}\right)^{\prime }du = - \sin{\left(u \right)} du$$$ (stegen kan ses »), och vi har att $$$\sin{\left(u \right)} du = - dv$$$.

Integralen blir

$$\frac{{\color{red}{\int{\sin{\left(u \right)} \sin{\left(\cos{\left(u \right)} \right)} d u}}}}{44} = \frac{{\color{red}{\int{\left(- \sin{\left(v \right)}\right)d v}}}}{44}$$

Tillämpa konstantfaktorregeln $$$\int c f{\left(v \right)}\, dv = c \int f{\left(v \right)}\, dv$$$ med $$$c=-1$$$ och $$$f{\left(v \right)} = \sin{\left(v \right)}$$$:

$$\frac{{\color{red}{\int{\left(- \sin{\left(v \right)}\right)d v}}}}{44} = \frac{{\color{red}{\left(- \int{\sin{\left(v \right)} d v}\right)}}}{44}$$

Integralen av sinus är $$$\int{\sin{\left(v \right)} d v} = - \cos{\left(v \right)}$$$:

$$- \frac{{\color{red}{\int{\sin{\left(v \right)} d v}}}}{44} = - \frac{{\color{red}{\left(- \cos{\left(v \right)}\right)}}}{44}$$

Kom ihåg att $$$v=\cos{\left(u \right)}$$$:

$$\frac{\cos{\left({\color{red}{v}} \right)}}{44} = \frac{\cos{\left({\color{red}{\cos{\left(u \right)}}} \right)}}{44}$$

Kom ihåg att $$$u=44 x$$$:

$$\frac{\cos{\left(\cos{\left({\color{red}{u}} \right)} \right)}}{44} = \frac{\cos{\left(\cos{\left({\color{red}{\left(44 x\right)}} \right)} \right)}}{44}$$

Alltså,

$$\int{\sin{\left(44 x \right)} \sin{\left(\cos{\left(44 x \right)} \right)} d x} = \frac{\cos{\left(\cos{\left(44 x \right)} \right)}}{44}$$

Lägg till integrationskonstanten:

$$\int{\sin{\left(44 x \right)} \sin{\left(\cos{\left(44 x \right)} \right)} d x} = \frac{\cos{\left(\cos{\left(44 x \right)} \right)}}{44}+C$$

$$$\int \sin{\left(44 x \right)} \sin{\left(\cos{\left(44 x \right)} \right)}\, dx = \frac{\cos{\left(\cos{\left(44 x \right)} \right)}}{44} + C$$$A