# Integration by parts

Source: https://projectalevel.co.uk/maths/calculus/integration_by_parts

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From the product rule, we can obtain the following formula, which is very useful in integration:

![](https://content.projectalevel.co.uk/img/maths/int.gif)

It is used when integrating the product of two numbers (a and b in the bottom formula).

![](https://content.projectalevel.co.uk/img/maths/int5.gif)