Integral dari $$$\frac{\sqrt{x^{2} - 1}}{x - 1}$$$

Temukan $$$\int \frac{\sqrt{x^{2} - 1}}{x - 1}\, dx$$$.

Misalkan $$$x=\cosh{\left(u \right)}$$$.

Maka $$$dx=\left(\cosh{\left(u \right)}\right)^{\prime }du = \sinh{\left(u \right)} du$$$ (langkah-langkah dapat dilihat »).

Selain itu, berlaku $$$u=\operatorname{acosh}{\left(x \right)}$$$.

Dengan demikian,

$$$\frac{\sqrt{x^{2} - 1}}{x - 1} = \frac{\sqrt{\cosh^{2}{\left( u \right)} - 1}}{\cosh{\left( u \right)} - 1}$$$

Gunakan identitas $$$\cosh^{2}{\left( u \right)} - 1 = \sinh^{2}{\left( u \right)}$$$:

$$$\frac{\sqrt{\cosh^{2}{\left( u \right)} - 1}}{\cosh{\left( u \right)} - 1}=\frac{\sqrt{\sinh^{2}{\left( u \right)}}}{\cosh{\left( u \right)} - 1}$$$

Dengan asumsi bahwa $$$\sinh{\left( u \right)} \ge 0$$$, diperoleh sebagai berikut:

$$$\frac{\sqrt{\sinh^{2}{\left( u \right)}}}{\cosh{\left( u \right)} - 1} = \frac{\sinh{\left( u \right)}}{\cosh{\left( u \right)} - 1}$$$

Integral menjadi

$${\color{red}{\int{\frac{\sqrt{x^{2} - 1}}{x - 1} d x}}} = {\color{red}{\int{\frac{\sinh^{2}{\left(u \right)}}{\cosh{\left(u \right)} - 1} d u}}}$$

Tulis ulang sinus hiperbolik dalam bentuk kosinus hiperbolik, tulis ulang pembilang lebih lanjut, gunakan rumus selisih dua kuadrat, dan sederhanakan:

$${\color{red}{\int{\frac{\sinh^{2}{\left(u \right)}}{\cosh{\left(u \right)} - 1} d u}}} = {\color{red}{\int{\left(\cosh{\left(u \right)} + 1\right)d u}}}$$

Integralkan suku demi suku:

$${\color{red}{\int{\left(\cosh{\left(u \right)} + 1\right)d u}}} = {\color{red}{\left(\int{1 d u} + \int{\cosh{\left(u \right)} d u}\right)}}$$

Terapkan aturan konstanta $$$\int c\, du = c u$$$ dengan $$$c=1$$$:

$$\int{\cosh{\left(u \right)} d u} + {\color{red}{\int{1 d u}}} = \int{\cosh{\left(u \right)} d u} + {\color{red}{u}}$$

Integral dari kosinus hiperbolik adalah $$$\int{\cosh{\left(u \right)} d u} = \sinh{\left(u \right)}$$$:

$$u + {\color{red}{\int{\cosh{\left(u \right)} d u}}} = u + {\color{red}{\sinh{\left(u \right)}}}$$

Ingat bahwa $$$u=\operatorname{acosh}{\left(x \right)}$$$:

$$\sinh{\left({\color{red}{u}} \right)} + {\color{red}{u}} = \sinh{\left({\color{red}{\operatorname{acosh}{\left(x \right)}}} \right)} + {\color{red}{\operatorname{acosh}{\left(x \right)}}}$$

Oleh karena itu,

$$\int{\frac{\sqrt{x^{2} - 1}}{x - 1} d x} = \sqrt{x - 1} \sqrt{x + 1} + \operatorname{acosh}{\left(x \right)}$$

Tambahkan konstanta integrasi:

$$\int{\frac{\sqrt{x^{2} - 1}}{x - 1} d x} = \sqrt{x - 1} \sqrt{x + 1} + \operatorname{acosh}{\left(x \right)}+C$$

$$$\int \frac{\sqrt{x^{2} - 1}}{x - 1}\, dx = \left(\sqrt{x - 1} \sqrt{x + 1} + \operatorname{acosh}{\left(x \right)}\right) + C$$$A