Integration by Substitution
Contents
Introduction to this topic[edit]
This page is dedicated to teaching techniques for integration by substitution. For other integration methods, see other sources.
The first section introduces the theory. Next comes a demonstration of the technique; this is followed by a section listing the steps used in that demonstration. The last section is a series of clarifying examples.
Assumed Knowledge[edit]
 Basic differentiation
 Basic integration methods
To understand the theory:
 Function composition: that a function can also be written as , which we call the composition of and .
 Chain rule
Theory of Integration by Substitution[edit]
This area is covered by the Wikipedia article Integration by substitution. On this page we deal with the practical aspects.
We begin with the following as is described by the Wikipedia article
This can be rewritten as
by setting
The principle applied here is function of a function (Function composition) and the reverse of the chain rule. This is the basis of integration by substitution.
The key skill now is to identify what value we use for and following the process to solution.
Integration by substitution[edit]
The objective of Integration by substitution is to substitute the integrand from an expression with variable to an expression with variable where
Theory
We want to transform the Integral from a function of to a function of
Starting with
Steps

(1) ie (2) ie (3) ie (4) ie Now equate with (5) ie (6) ie (7) ie We have achieved our desired result
Procedure
 Calculate
 Calculate which is and make sure you express the result in terms of the variable
 Calculate
 Calculate
Technique[edit]
Example 1[edit]
Let us examine this integral
The inner function is
The outer function is
Recognising this relationship we then move onto the following set of steps to process the inner function
NOTE: that the differential of is .
Now we substitute and into the original integral.
Then apply standard integral technique
And finally we substitute the value of back into the equation
Example 2[edit]
Let us examine this integral
We can first rearrange the fraction to make it more familiar.
The inner function is
The outer function is
Next we assign and
But we have a problem! doesnt equal ! So we need to rearrange our formula for .
Now we can substitute and into the original integral.
Study the above substitution carefully. We moved the fractional component of du to the front as it represents a constant.
Now apply standard integral technique
Cleaning up this expression we have
And finally we substitute the value of u back into the equation
The Definite Integral[edit]
Consider the definite integral
By using the substitution
Now because we have limits, we need to change them with respect to . Note the value of the limits.
Now we have a new definite integral to solve
The Steps We Applied[edit]
Let's now review the steps for integration by substitution.
Indefinite Integral  Definite Integral  

1.  First identify that you have a function of a function. This skill comes with practice to identify candidates.  First identify that you have a function of a function. This skill comes with practice to identify candidates. 
2.  Identify and then find that is appropriate for the expression.  Identify and then find that is appropriate for the expression. 
3.  Change limits for definite integrals.  
4.  Integrate using normal techniques.  Integrate using normal techniques. 
5.  Substitute back the values for u for indefinite integrals.  
6.  Don't forget the constant of integration for indefinite integrals. 
Finding u[edit]
Let's look at more examples at finding .
Example 1[edit]
Example 2[edit]
Here we first perform the substitution , so that
With this, we get