Integral of $$$\tan^{5}{\left(x \right)}$$$

Let $$$u=\tan{\left(x \right)}$$$.

Then $$$x=\operatorname{atan}{\left(u \right)}$$$ and $$$dx=\left(\operatorname{atan}{\left(u \right)}\right)^{\prime }du = \frac{du}{u^{2} + 1}$$$ (steps can be seen »).

Therefore,

$${\color{red}{\int{\tan^{5}{\left(x \right)} d x}}} = {\color{red}{\int{\frac{u^{5}}{u^{2} + 1} d u}}}$$

Since the degree of the numerator is not less than the degree of the denominator, perform polynomial long division (steps can be seen »):

$${\color{red}{\int{\frac{u^{5}}{u^{2} + 1} d u}}} = {\color{red}{\int{\left(u^{3} - u + \frac{u}{u^{2} + 1}\right)d u}}}$$

Integrate term by term:

$${\color{red}{\int{\left(u^{3} - u + \frac{u}{u^{2} + 1}\right)d u}}} = {\color{red}{\left(- \int{u d u} + \int{u^{3} d u} + \int{\frac{u}{u^{2} + 1} d u}\right)}}$$

Apply the power rule $$$\int u^{n}\, du = \frac{u^{n + 1}}{n + 1}$$$ $$$\left(n \neq -1 \right)$$$ with $$$n=3$$$:

$$- \int{u d u} + \int{\frac{u}{u^{2} + 1} d u} + {\color{red}{\int{u^{3} d u}}}=- \int{u d u} + \int{\frac{u}{u^{2} + 1} d u} + {\color{red}{\frac{u^{1 + 3}}{1 + 3}}}=- \int{u d u} + \int{\frac{u}{u^{2} + 1} d u} + {\color{red}{\left(\frac{u^{4}}{4}\right)}}$$

Apply the power rule $$$\int u^{n}\, du = \frac{u^{n + 1}}{n + 1}$$$ $$$\left(n \neq -1 \right)$$$ with $$$n=1$$$:

$$\frac{u^{4}}{4} + \int{\frac{u}{u^{2} + 1} d u} - {\color{red}{\int{u d u}}}=\frac{u^{4}}{4} + \int{\frac{u}{u^{2} + 1} d u} - {\color{red}{\frac{u^{1 + 1}}{1 + 1}}}=\frac{u^{4}}{4} + \int{\frac{u}{u^{2} + 1} d u} - {\color{red}{\left(\frac{u^{2}}{2}\right)}}$$

Let $$$v=u^{2} + 1$$$.

Then $$$dv=\left(u^{2} + 1\right)^{\prime }du = 2 u du$$$ (steps can be seen »), and we have that $$$u du = \frac{dv}{2}$$$.

Therefore,

$$\frac{u^{4}}{4} - \frac{u^{2}}{2} + {\color{red}{\int{\frac{u}{u^{2} + 1} d u}}} = \frac{u^{4}}{4} - \frac{u^{2}}{2} + {\color{red}{\int{\frac{1}{2 v} d v}}}$$

Apply the constant multiple rule $$$\int c f{\left(v \right)}\, dv = c \int f{\left(v \right)}\, dv$$$ with $$$c=\frac{1}{2}$$$ and $$$f{\left(v \right)} = \frac{1}{v}$$$:

$$\frac{u^{4}}{4} - \frac{u^{2}}{2} + {\color{red}{\int{\frac{1}{2 v} d v}}} = \frac{u^{4}}{4} - \frac{u^{2}}{2} + {\color{red}{\left(\frac{\int{\frac{1}{v} d v}}{2}\right)}}$$

The integral of $$$\frac{1}{v}$$$ is $$$\int{\frac{1}{v} d v} = \ln{\left(\left|{v}\right| \right)}$$$:

$$\frac{u^{4}}{4} - \frac{u^{2}}{2} + \frac{{\color{red}{\int{\frac{1}{v} d v}}}}{2} = \frac{u^{4}}{4} - \frac{u^{2}}{2} + \frac{{\color{red}{\ln{\left(\left|{v}\right| \right)}}}}{2}$$

Recall that $$$v=u^{2} + 1$$$:

$$\frac{u^{4}}{4} - \frac{u^{2}}{2} + \frac{\ln{\left(\left|{{\color{red}{v}}}\right| \right)}}{2} = \frac{u^{4}}{4} - \frac{u^{2}}{2} + \frac{\ln{\left(\left|{{\color{red}{\left(u^{2} + 1\right)}}}\right| \right)}}{2}$$

Recall that $$$u=\tan{\left(x \right)}$$$:

$$\frac{\ln{\left(1 + {\color{red}{u}}^{2} \right)}}{2} - \frac{{\color{red}{u}}^{2}}{2} + \frac{{\color{red}{u}}^{4}}{4} = \frac{\ln{\left(1 + {\color{red}{\tan{\left(x \right)}}}^{2} \right)}}{2} - \frac{{\color{red}{\tan{\left(x \right)}}}^{2}}{2} + \frac{{\color{red}{\tan{\left(x \right)}}}^{4}}{4}$$

Therefore,

$$\int{\tan^{5}{\left(x \right)} d x} = \frac{\ln{\left(\tan^{2}{\left(x \right)} + 1 \right)}}{2} + \frac{\tan^{4}{\left(x \right)}}{4} - \frac{\tan^{2}{\left(x \right)}}{2}$$

Add the constant of integration:

$$\int{\tan^{5}{\left(x \right)} d x} = \frac{\ln{\left(\tan^{2}{\left(x \right)} + 1 \right)}}{2} + \frac{\tan^{4}{\left(x \right)}}{4} - \frac{\tan^{2}{\left(x \right)}}{2}+C$$

$$$\int \tan^{5}{\left(x \right)}\, dx = \left(\frac{\ln\left(\tan^{2}{\left(x \right)} + 1\right)}{2} + \frac{\tan^{4}{\left(x \right)}}{4} - \frac{\tan^{2}{\left(x \right)}}{2}\right) + C$$$A