Practice, practice, practice. Theory is not everything. You need to apply what you learn from reading. These exercises will help you improve your “integration skills” by putting into practice what you’ve leant here https://addjustabitofpi.com/integration-techniques-integration-by-parts/ about integration by parts. If you don’t remember the basic integrals and their rules, click on these two links: https://addjustabitofpi.com/2019/10/03/fundamental-integrals/ https://addjustabitofpi.com/2019/10/03/rules-and-properties-of-integrals/. Check your results here: https://addjustabitofpi.com/2019/10/09/integration-by-parts-solution-with-procedure/.
Here are some indefinite integrals you can practice with using u-sub. If you can’t solve all of them, don’t discourage. You can see the procedure for each here: https://addjustabitofpi.com/category/solutions/. This will help you understand the logics of integrals and you will eventually get the hang of it and be able to solve them right away! If you don’t remember the rules and properties of integrals, click this link: https://addjustabitofpi.com/rules-and-properties-of-integrals/. Notice that cot (cotangent) is the reciprocal of tan (tangent), which means that cot(x)=cos(x)/sin(x). Remember that sec (secant) is the reciprocal… Read more U-substitution | Exercises →