Integration of substitution is also known as U – Substitution, this method helps in solving the process of integration function.

When a function cannot be integrated directly, then this process is used. To integration by substitution is used in the following steps:

• A new variable is to be chosen, let’s name t “x”
• The value of dx is to is to be determined.
• Substitution is done
• Integral function is to be integrated
• Initial variable x, to be returned.

The standard formula for integration is given as:

$$\int f(ax+b)dx=\frac{1}{a}\phi (ax+b)+c$$

$$\int f\left(x^n\right)x^{n-1}dx=\frac{1}{n}\varphi \left(x^n\right)+c$$

$$\int \frac{f^{\prime }(x)}{f(x)}dx=logf(x)+c$$

Solved Examples

Question: Find the integration using the substitution formula: 

Solution

Let u = 3 + ln 2x
We can expand out the log term on the right hand side as: 3 + ln 2x = 3 + ln 2 + ln x

The first 2 terms on the right are constants (whose derivative equals zero) and the derivative of the natural log of x is

.

Then: