# Definite Integration by Substitution

\begin{align} \displaystyle u &= f(x) \\ du &= \dfrac{du}{dx} \times dx \\ \end{align} Converting $x$-values to corresponding $u$-values are required.

### Example 1

Find $\displaystyle 2\int_{0}^{1}{\sqrt{2x+1}}dx$. It is not required converting $x$-values to corresponding $u$-values, but substitute $x$-values after integrating it.

### Example 2

Find $\displaystyle \int_{0}^{1}{x\sqrt{1+x^2}}dx$.

### Example 3

Find $\displaystyle \int_{0}^{1}{(x^2+3x)^4(2x+3)}dx$.