What i want to learn more about chapter 2.1?

I wish to learn the more difficult questions on chapter 2.1. By doing this, i can challenge myself to go to a higher level. Now that i have understood the basics of chapter 2.1, i now want to go on and slowly try to understand the more difficult questions. If there is any other mothod to get the answer, i would love to learn it. If i could not understand the other method, i might as well stick to the easier method.