1
Solved example of Integration by trigonometric substitution
$\int\sqrt{x^2+4}dx$
2
Solve the integral $\int\sqrt{x^2+4}dx$ by trigonometric substitution using the substitution
$\begin{matrix}x=2\tan\left(\theta\right) \\ dx=2\sec\left(\theta\right)^2d\theta\end{matrix}$
3
Substituting in the original integral, we get
$\int2\sqrt{4\tan\left(\theta\right)^2+4}\sec\left(\theta\right)^2d\theta$
4
Take the constant out of the integral
$2\int\sqrt{4\tan\left(\theta\right)^2+4}\sec\left(\theta\right)^2d\theta$
5
Factor by the greatest common divisor $4$
$2\int\sqrt{4\left(\tan\left(\theta\right)^2+1\right)}\sec\left(\theta\right)^2d\theta$
6
The power of a product is equal to the product of it's factors raised to the same power
$2\int2\sqrt{\tan\left(\theta\right)^2+1}\sec\left(\theta\right)^2d\theta$
7
Applying the trigonometric identity: $\tan(x)^2+1=\sec(x)^2$
$2\int2\sec\left(\theta\right)^2\sec\left(\theta\right)d\theta$
8
Take the constant out of the integral
$4\int\sec\left(\theta\right)^2\sec\left(\theta\right)d\theta$
9
When multiplying exponents with same base you can add the exponents
$4\int\sec\left(\theta\right)^{3}d\theta$
10
Simplify the integral of secant applying the reduction formula, $\displaystyle\int\sec(x)^{n}dx=\frac{\sin(x)\sec(x)^{n-1}}{n-1}+\frac{n-2}{n-1}\int\sec(x)^{n-2}dx$
$4\left(\frac{\sec\left(\theta\right)^{2}\sin\left(\theta\right)}{2}+\frac{1}{2}\int\sec\left(\theta\right)d\theta\right)$
11
Expressing the result of the integral in terms of the original variable
$4\left(\frac{\frac{\left(\frac{\sqrt{x^2+4}}{2}\right)^{2}x}{\sqrt{x^2+4}}}{2}+\frac{1}{2}\int\sec\left(\theta\right)d\theta\right)$
12
Simplifying the fraction
$4\left(\frac{\left(\frac{\sqrt{x^2+4}}{2}\right)^{2}x}{2\sqrt{x^2+4}}+\frac{1}{2}\int\sec\left(\theta\right)d\theta\right)$
13
Take out the constant $2$ from the fraction's denominator
$4\left(\frac{1}{2}\left(\frac{\left(\frac{\sqrt{x^2+4}}{2}\right)^{2}x}{\sqrt{x^2+4}}\right)+\frac{1}{2}\int\sec\left(\theta\right)d\theta\right)$
14
The integral of the secant function is given by the following formula, $\displaystyle\int\sec(x)dx=\ln\left|\sec(x)+\tan(x)\right|$
$4\left(\frac{1}{2}\left(\frac{\left(\frac{\sqrt{x^2+4}}{2}\right)^{2}x}{\sqrt{x^2+4}}\right)+\frac{1}{2}\ln\left|\sec\left(\theta\right)+\tan\left(\theta\right)\right|\right)$
15
Expressing the result of the integral in terms of the original variable
$4\left(\frac{\frac{1}{2}\left(\frac{\sqrt{x^2+4}}{2}\right)^{2}x}{\sqrt{x^2+4}}+\frac{1}{2}\ln\left|\frac{\sqrt{x^2+4}}{2}+\frac{x}{2}\right|\right)$
16
Add fraction's numerators with common denominators: $\frac{\sqrt{x^2+4}}{2}$ and $\frac{x}{2}$
$4\left(\frac{\frac{1}{2}\left(\frac{\sqrt{x^2+4}}{2}\right)^{2}x}{\sqrt{x^2+4}}+\frac{1}{2}\ln\left|\frac{\sqrt{x^2+4}+x}{2}\right|\right)$
17
As the integral that we are solving is an indefinite integral, when we finish we must add the constant of integration
$4\left(\frac{\frac{1}{2}\left(\frac{\sqrt{x^2+4}}{2}\right)^{2}x}{\sqrt{x^2+4}}+\frac{1}{2}\ln\left|\frac{\sqrt{x^2+4}+x}{2}\right|\right)+C_0$