Wize University Calculus 1 Textbook > Integrals
Integration by Substitution (U-Substitution)
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Integration by Substitution (U-Substitution)
There is no "Chain Rule for Integrals" like there is for derivatives. When we are trying to integrate compositions of functions, often we use the technique of U Substitution.
U Substitution
If is a differentiable function with a continuous derivative , by letting we have
Wize Tip
We typically use U-Substitution when the derivative of one part shows up elsewhere in the integral.
Procedure for U-Substitution
- Let equal part of the integrand (usually what's inside parenthesis or the "messy" part of the function)
- Differentiate to get
- Solve for
- Substitute and into your integral (for definite integrals replace the bounds)
- Integrate with respect to
- Substitute the original expression back in (only for indefinite integrals)

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Example: U-Sub
Evaluate the following definite integral
.
1. Pick "u" expression
We have 2 candidates for : and
Both of these are wrapped inside brackets, let's pick the higher degree part:
2. Differentiate u to get du=...dx
3. Solve for dx
4. Substitute u and replace dx
(Since this is a definite integral, we need to replace the bounds)
When the lower bound is
When the upper bound is
Let's substitute in the expression, the bounds, and replace the expression:
5. Integrate this new u expression
Wize Tip
Since this is a definite integral, we don't have to substitute the original x expression back in.

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Example: U Sub
Evaluate the following definite integral
Notice that , which is similar to the that appears outside the square root.
1. Pick "u" expression
2. Differentiate u to get du
3. Solve for dx
4. Substitute u and replace dx
(Since this is a definite integral, we need to replace the bounds)
So then
5. Integrate this new u expression

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Example: U-Sub (with back-substitution)
Evaluate the following indefinite integral
Simplifying will not make this integration any easier, let's try u-substitution.
Normally, we will pick u to be the numerator because the numerator is of degree 3 and denominator is of degree 2. However, if you try that, you'll realize that we have nothing to cancel out with in our 4th step. So instead, let's pick u to be the denominator.
1. Pick "u" expression
2. Differentiate u to get du
3. Solve for dx
4. Substitute u and replace dx
Since the expression still involves an x term, we need to back-substitute:
From , we have .
We can now use this to replace the in our expression:
5. Integrate this new u expression
6. Sub the x expression back in for u:
*Since for all values of x, we don't need the absolute value signs.
Practice: U-Sub
Evaluate the following indefinite integral
Practice: U-Sub
Evaluate the following indefinite integral
Practice: U-Sub
Evaluate the following indefinite integral
Practice: U-Sub
Evaluate the following indefinite integral
Extra Practice
Practice: Substitution with Definite Integral
Practice: Substitution with Definite Integral
Evaluate .
Practice: Substitution with Definite Integral
Practice: Substitution with Definite Integral
Evaluate .
Practice: Substitution with Definite Integral
Practice: Substitution with Definite Integral
Evaluate .