Integraal van $$$\cos{\left(x^{2} - 5 \right)}$$$

Bepaal $$$\int \cos{\left(x^{2} - 5 \right)}\, dx$$$.

Herschrijf de integraand:

$${\color{red}{\int{\cos{\left(x^{2} - 5 \right)} d x}}} = {\color{red}{\int{\left(\sin{\left(5 \right)} \sin{\left(x^{2} \right)} + \cos{\left(5 \right)} \cos{\left(x^{2} \right)}\right)d x}}}$$

Integreer termgewijs:

$${\color{red}{\int{\left(\sin{\left(5 \right)} \sin{\left(x^{2} \right)} + \cos{\left(5 \right)} \cos{\left(x^{2} \right)}\right)d x}}} = {\color{red}{\left(\int{\sin{\left(5 \right)} \sin{\left(x^{2} \right)} d x} + \int{\cos{\left(5 \right)} \cos{\left(x^{2} \right)} d x}\right)}}$$

Pas de constante-veelvoudregel $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ toe met $$$c=\cos{\left(5 \right)}$$$ en $$$f{\left(x \right)} = \cos{\left(x^{2} \right)}$$$:

$$\int{\sin{\left(5 \right)} \sin{\left(x^{2} \right)} d x} + {\color{red}{\int{\cos{\left(5 \right)} \cos{\left(x^{2} \right)} d x}}} = \int{\sin{\left(5 \right)} \sin{\left(x^{2} \right)} d x} + {\color{red}{\cos{\left(5 \right)} \int{\cos{\left(x^{2} \right)} d x}}}$$

Deze integraal (Fresnel-cosinusintegraal) heeft geen gesloten vorm:

$$\int{\sin{\left(5 \right)} \sin{\left(x^{2} \right)} d x} + \cos{\left(5 \right)} {\color{red}{\int{\cos{\left(x^{2} \right)} d x}}} = \int{\sin{\left(5 \right)} \sin{\left(x^{2} \right)} d x} + \cos{\left(5 \right)} {\color{red}{\left(\frac{\sqrt{2} \sqrt{\pi} C\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right)}{2}\right)}}$$

Pas de constante-veelvoudregel $$$\int c f{\left(x \right)}\, dx = c \int f{\left(x \right)}\, dx$$$ toe met $$$c=\sin{\left(5 \right)}$$$ en $$$f{\left(x \right)} = \sin{\left(x^{2} \right)}$$$:

$$\frac{\sqrt{2} \sqrt{\pi} \cos{\left(5 \right)} C\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right)}{2} + {\color{red}{\int{\sin{\left(5 \right)} \sin{\left(x^{2} \right)} d x}}} = \frac{\sqrt{2} \sqrt{\pi} \cos{\left(5 \right)} C\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right)}{2} + {\color{red}{\sin{\left(5 \right)} \int{\sin{\left(x^{2} \right)} d x}}}$$

Deze integraal (Fresnel-sinusintegraal) heeft geen gesloten vorm:

$$\frac{\sqrt{2} \sqrt{\pi} \cos{\left(5 \right)} C\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right)}{2} + \sin{\left(5 \right)} {\color{red}{\int{\sin{\left(x^{2} \right)} d x}}} = \frac{\sqrt{2} \sqrt{\pi} \cos{\left(5 \right)} C\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right)}{2} + \sin{\left(5 \right)} {\color{red}{\left(\frac{\sqrt{2} \sqrt{\pi} S\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right)}{2}\right)}}$$

Dus,

$$\int{\cos{\left(x^{2} - 5 \right)} d x} = \frac{\sqrt{2} \sqrt{\pi} \cos{\left(5 \right)} C\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right)}{2} + \frac{\sqrt{2} \sqrt{\pi} \sin{\left(5 \right)} S\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right)}{2}$$

Vereenvoudig:

$$\int{\cos{\left(x^{2} - 5 \right)} d x} = \frac{\sqrt{2} \sqrt{\pi} \left(\cos{\left(5 \right)} C\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right) + \sin{\left(5 \right)} S\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right)\right)}{2}$$

Voeg de integratieconstante toe:

$$\int{\cos{\left(x^{2} - 5 \right)} d x} = \frac{\sqrt{2} \sqrt{\pi} \left(\cos{\left(5 \right)} C\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right) + \sin{\left(5 \right)} S\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right)\right)}{2}+C$$

$$$\int \cos{\left(x^{2} - 5 \right)}\, dx = \frac{\sqrt{2} \sqrt{\pi} \left(\cos{\left(5 \right)} C\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right) + \sin{\left(5 \right)} S\left(\frac{\sqrt{2} x}{\sqrt{\pi}}\right)\right)}{2} + C$$$A