Tips

1. Before you doing a substitution, observe which part of the function is the derivative of the other part of this function.
2. If the function is not so clear that you cannot find out the substitution immediately. Make some tries instead of doing nothing and you may find idea during this process.
3. Remember the derivative of those important function, such as sin or cos, to help you find out the substitution faster and it can also save your time in a exam.